Donald Trump made a promise to white evangelical Christians, whose support can seem mystifying to the outside observer.

SIOUX CENTER, Iowa — They walked to the sanctuary in the frozen silence before dawn, footsteps crunching over the snow. Soon, hundreds joined in line. It was January 2016, and the unlikely Republican front-runner, Donald J. Trump, had come to town.

He was the boastful, thrice-married, foul-mouthed star of “The Apprentice.” They were one of the most conservative Christian communities in the nation, with 19 churches in a town of about 7,500 people.

Many were skeptical, and came to witness the spectacle for themselves. A handful stood in silent protest. But when the doors opened and the pews filled, Mr. Trump’s fans welcomed him by chanting his name. A man waved a “Silent Majority Stands With Trump” sign. A woman pointed a lone pink fingernail up to the sky.

In his dark suit and red tie, Mr. Trump stood in front of a three-story-tall pipe organ and waved his arms in time with their shouts: Trump, Trump, Trump.

The 67-minute speech Mr. Trump gave that day at Dordt University, a Christian college in Sioux Center, would become infamous, instantly covered on cable news and to this day still invoked by his critics. But the line that gained notoriety — the promise that he “could stand in the middle of Fifth Avenue and shoot somebody” and “wouldn’t lose any voters” — overshadowed another message that morning.

“I will tell you, Christianity is under tremendous siege, whether we want to talk about it or we don’t want to talk about it,” Mr. Trump said.

Christians make up the overwhelming majority of the country, he said. And then he slowed slightly to stress each next word: “And yet we don’t exert the power that we should have.”

If he were elected president, he promised, that would change. He raised a finger.

“Christianity will have power,” he said. “If I’m there, you’re going to have plenty of power, you don’t need anybody else. You’re going to have somebody representing you very, very well. Remember that.”

Nine days later, the Iowa caucuses kicked off the most polarizing road to the White House in memory. Mr. Trump largely lost the evangelicals of Sioux County that day: Only 11 percent of Republicans caucused for him. But when November came, they stood by him en masse: 81 percent of the county voted for him. And so did 81 percent of white evangelical voters nationwide.

Now, this group could be Mr. Trump’s best chance at re-election. The president’s response to the coronavirus pandemic has battered his political standing: He has trailed Joseph R. Biden Jr., the presumptive Democratic nominee, by nearly double digits for a month in national polls. Even among white evangelicals, his approval rating has dipped slightly. But 82 percent say they intend to vote for him, according to the Pew Research Center.

To the outside observer, the relationship between white evangelical Christians and Donald Trump can seem mystifying.

From the start it appeared an impossible contradiction. Evangelicals for years have defined themselves as the values voters, people who prized the Bible and sexual morality — and loving your neighbor as yourself — above all.

Donald Trump was the opposite. He bragged about assaulting women. He got divorced, twice. He built a career off gambling. He cozied up to bigots. He rarely went to church. He refused to ask for forgiveness.

It is a contradiction that has held for four years. They stood by him when he shut out Muslim refugees. When he separated children from their parents at the border. When he issued brash insults over social media. When he uttered falsehoods as if they were true. When he was impeached.

Theories, and rationalizations, abound:

That evangelical support was purely transactional.

That they saw him as their best chance in decades to end legalized abortion.

That the opportunity to nominate conservative justices to the Supreme Court was paramount.

That they hated Hillary Clinton, or felt torn to pick the lesser of two evils.

That they held their noses and voted, hoping he would advance their policy priorities and accomplish their goals.

But beneath all this, there is another explanation. One that is more raw and fundamental.

Evangelicals did not support Mr. Trump in spite of who he is. They supported him because of who he is, and because of who they are. He is their protector, the bully who is on their side, the one who offered safety amid their fears that their country as they know it, and their place in it, is changing, and changing quickly. White straight married couples with children who go to church regularly are no longer the American mainstream. An entire way of life, one in which their values were dominant, could be headed for extinction. And Mr. Trump offered to restore them to power, as though they have not been in power all along.

“You are always only one generation away from losing Christianity,” said Micah Schouten, who was born and raised in Sioux Center, recalling something a former pastor used to say. “If you don’t teach it to your children it ends. It stops right there.”

Ultimately Mr. Trump recognized something, said Lisa Burg, a longtime resident of nearby Orange City. It is a reason she thinks people will still support him in November.

“The one group of people that people felt like they could dis and mock and put down had become the Christian. Just the middle-class, middle-American Christians,” Ms. Burg said. “That was the one group left that you could just totally put down and call deplorable. And he recognized that, You know what? Yeah, it’s OK that we have our set of values, too. I think people finally said, ‘Yes, we finally have somebody that’s willing to say we’re not bad, we need to have a voice too.’”

Explained Jason Mulder, who runs a small design company in Sioux Center: “I feel like on the coasts, in some of the cities and stuff, they look down on us in rural America. You know, we are a bunch of hicks, and don’t know anything. They don’t understand us the same way we don’t understand them. So we don’t want them telling us how to live our lives.”

He added: “You joke that we don’t get it, well, you don’t get it either. We are not speaking the same language.”

The speech in Sioux Center symbolized why there has been so much confusion about evangelical support for Mr. Trump. From the beginning, the outside world focused on the comment about shooting someone on Fifth Avenue. Those in the town, though, ultimately heard something else entirely. What mattered was not just what Mr. Trump said. It was where he said it. And to whom.

And so to understand the relationship, one has to go back to Jan. 23, 2016. One has to hear the speech at Dordt the way the evangelical community heard it.

‘We started out as a Christian nation’

The day Mr. Trump spoke at Dordt, Rob Driesen sat in the very front. He supported Ted Cruz at the time. But now, four years later, his eyes light up when he talks about Mr. Trump.

He brought out two photographs, framed, one of him and Mr. Trump, and one of him with Mike Pence before he became vice president.

“I guess the biggest concern for me is trying to keep our country the way it was. Conservative. The values. For us, I mean, this is as good as it gets. We can do whatever we want,” said Mr. Driesen, 56, sitting at his kitchen table this spring with his wife, Cheryl, 52. Next to them, a family motto was painted on the wall in gold and black lettering: “Home, Where Your Story Begins.”

He gestured to his front door. “You don’t lock the doors,” he said. “I never take the keys out of the car.”

He thought back to Mr. Trump’s speech. “There was one gaffe he kind of got in trouble for. What was it? Because there were a bunch of things he said.” He paused a while. “I can’t distinctly remember, but I just remember there was one thing, and that was the news for 10 days after that. Something about — I wish I could remember. I can’t.”

“You know how things can sound bad,” he said. “He can get away with it. People seemed to like it.”

Mr. Driesen works for the utility company, and his wife is a nurse. They have raised their five children in the area, where they grew up. Mr. Driesen’s grandmother’s grandparents were among the first Protestant immigrants to come to Iowa from the Netherlands in the late 1800s. They were among hundreds of families looking for economic opportunity, and a place to worship without interference from the Dutch government. The immigrants called their first colony Pella, after the place where first-century Christians fled to avoid persecution. Their second colony, which would include Sioux Center, settled on land that had been home to the Yankton Sioux, before the U.S. government had forced them west.

Church is still what really holds the community together. A day earlier, on Sunday, the Driesens had gone to services in the morning and at night. They unplugged the router and turned off their cellphones. They read the Bible. Sioux Center was quiet on Sundays, when it is easier to name what is open — the Pizza Hut, the Culver’s, the Walmart — than what is not.

Mr. Driesen spoke of the policies that were important to him, all the usual conservative issues. Small government. Ending abortion. Judges who share his political views. “Traditional families,” he said.

“Unfortunately, there’s just more divorce than there used to be,” he said. “There’s more cohabitating. I think it is detrimental to the family. I just think kids do better in a two-parent home, with a mom and a dad.”

His wife had been quiet, letting him do the talking. She did not go to Mr. Trump’s speech, and politics were not her thing; often the men around here were more vocal than their wives about supporting the president. Now she spoke up.

“The religious part is huge for us, as we see religious freedoms being taken away,” Ms. Driesen said. “If you don’t believe in homosexuality or something, you lose your business because of it. And that’s a core part of your faith. Whereas I see Trump as defending that. He’s actually made that executive order to put the Bibles back in the public schools. That is something very worrisome and dear to us, our religious freedom.”

She remembered how when her mother was a child about 20 miles north, the public school still started the day with prayer. But when she was growing up, it stopped. Her church, Netherlands Reformed, started a private Christian school in Rock Valley, and so she went there instead.

They send their children to that same school, which still has some of the same teachers.

“We don’t know any different,” Mr. Driesen said. “For a lot of people around here, that’s just what you do. You have the same classmates all the way through. And it holds the community together.” His siblings left the area for a while, but then they came back.

They want the Christian education for their children “so we don’t have to have them indoctrinated with all these different things,” he said. “We are free to teach them our values.”

“So far,” Ms. Driesen clarified. “That’s where we see Trump as a key figure to keep that freedom.”

She paused. “It’s almost like it is a reverse intolerance. If you have somebody that’s maybe on the liberal side, they say that we are intolerant of them. But it is inverse intolerant if we can’t live out our faith.”

She worried that the school might be forced to let in students who were not Christian, or hire teachers who were gay.

“Silly things. Just let the boys go in the boys’ bathroom and the girls go in the girls’,” he said. “It’s just something you’d think is never going to happen, and nowadays it could. And it probably will.”

“Just hope nobody turns it upside down,” he said.

“But we feel like we are in a little area where we are protected yet,” she said. “We are afraid of losing that, I guess.”

Every day, Mr. Driesen said, they pray. He wakes up and prays for his family, and for safety at his job at Rural Electric Cooperative. Often he would pray that when he hooked up a transformer it would not blow up.

They want America to be a Christian nation for their children. “We started out as a Christian nation,” she said.

“You can’t make people do these things,” he said. “But you can try to protect what you’ve got, you might say.”

He thought about November, and felt confident Mr. Trump would win. He sees Trump flags all over as he drives. Something has shifted in the country, he said, and he is looking ahead to who might even come after Mr. Trump.

“I feel like we are safe for four more years,” he said. “You know. So that’s a good feeling.”

‘He will vanquish all our foes’

Micah Schouten cannot remember exactly why he did not go to hear Mr. Trump that morning. Probably it was just too cold, or maybe he was working.

As a child he dreamed of being a farmer like his father, but land was too expensive. Now he worked at a cattle reproduction company — or, as he explained with a smile, “I.V.F. for cows.”

At the time, he supported Ben Carson. But Mr. Trump was a celebrity, and Dordt University, 10 minutes down the road, was Mr. Schouten’s alma mater. The school was named for a major church assembly in 1618 and 1619 that declared salvation was only for God’s chosen ones, and expelled from Dutch territory anyone who disagreed. Its students are “Dordt Defenders,” represented by a knight in gray armor, wielding a sword like a cross.

So that night, after his three children went to bed, Mr. Schouten pulled up YouTube to hear it for himself.

Soon Mr. Trump made him laugh. The candidate bashed the media. He said the thing about shooting someone on Fifth Avenue. But the thing Mr. Schouten remembered most was that he defended Christianity.

Mr. Schouten, 36, is proud of his town and during a tour pointed out a community hospital and water park for children. Asked about the growing Latino population in Sioux Center, he drove to an area he did not know well and pointed out a trailer park where he said new arrivals, many of them Latino workers, live.

When he was a child, he said, the public school students were almost entirely white, and now about half of the kindergartners are Hispanic. He noticed that many of the Latinos in town were Catholic, and that they worked or shopped on Sunday, which was traditionally a time of rest in Sioux Center.

“You can’t find a single white person to milk cows or do any of that stuff,” he said. “They know how to work hard. They don’t mind working those 12-hour shifts.”

On a Sunday in March, Mr. Schouten worshiped at United Reformed Church with neighbors he has known for years. They all knew the harmonies by heart. They were one choir, in sync on yellow quilted pews.

They sang: “I will praise my dear Redeemer, his triumphant power I’ll tell, how the victory he giveth over sin and death and hell.”

They prayed: “With our God we shall be valiant, he will vanquish all our foes.”

The pastor spoke to a sea of white parishioners: “God’s standard requires absolute, total, perfect, obedience.”

The Schoutens’ oldest daughter, who was 11, took careful notes in her journal.

When the service ended, the church served cookies. Mr. Schouten caught up with some friends, all fathers in their 30s wearing blue collared shirts and khaki pants.

“Trump’s an outsider, like the rest of us,” he said. “We might not respect Trump, but we still love the guy for who he is.”

“Is he a man of integrity? Absolutely not,” he went on. “Does he stand up for some of our moral Christian values? Yes.”

The guys agreed. “I’m not going to say he’s a Christian, but he just doesn’t attack us,” his friend Jason Mulder said.

Mr. Schouten’s wife, Caryn, had walked over with the other wives. After the election of President Barack Obama, the country seemed to undergo a cultural shift, she said. “It was dangerous to voice your Christianity,” she said. “Because we were viewed as bigots, as racists — we were labeled as the haters and the ones who are causing all the derision and all of the problems in America. Blame it on the white believers.”

None of them said they had wanted to vote for Mr. Trump, but they did — “When he was the last option,” Heather Hoogendoorn said. The group laughed.

But they agreed it would be easier to vote for him this time. Before, it was hard to know what he would be like as president. Now they knew, and they liked the results: Supreme Court justices, conservative judges, including a Dordt graduate now on the U.S. Court of Appeals for the Eighth Circuit, and growing clout for the anti-abortion movement.

“Obama wanted to take my assault rifle, he wanted to take out all the high-capacity magazines,” Mr. Schouten said. “It just —”

“— felt like your freedoms kept getting taken from you,” said Heather’s husband, Paul, finishing the sentence for him.

When the Schoutens got home, Caryn, 36, scooped a chip into sour cream dip and plopped into a chair in her living room.

She spoke of her concern about sex trafficking. She had seen posts on Facebook about mothers being followed to their cars if they went shopping at Target in Sioux City, almost an hour away.

“I’m safe when I’m here. I’m not afraid when I’m here,” she said.

They thought about the lives they want for their children, and why they send them to a Christian elementary school. “We hope our kids eventually find a Christian spouse, and that exposes them to other kids of like-mindedness,” her husband said. The two of them met through their rival Christian high schools.

People seem to get married younger around here than they do in corporate America, Mr. Schouten said. “It’s fairly common for women to go to Dordt to get their M.R.S. degree, their Mrs. degree,” he said.

When she was younger, his wife said, she used to say she would leave Sioux County. She remembered the shock of traveling to Europe in high school and seeing “men in full drag” for the first time.

“We have life very easy, it is laid back, it is like-minded people. And it’s just, I like the bubble,” she said. “I like not worrying about sending them outside to play, or whose house they are going to if they are going to the neighbors a few houses down, they might not go to the same church, they might not hold all the same beliefs, but I trust them. I don’t know, maybe that is naïve.”

The years of the Obama presidency were confusing to her. She said she heard talk of giving freedoms to gay people and members of minority groups. But to her it felt like her freedoms were being taken away. And that she was turning into the minority.

“I do not love Trump. I think Trump is good for America as a country. I think Trump is going to restore our freedoms, where we spent eight years, if not more, with our freedoms slowly being taken away under the guise of giving freedoms to all,” she said. “Caucasian-Americans are becoming a minority. Rapidly.”

She explained what she meant. “If you are a hard-working Caucasian-American, your rights are being limited because you are seen as against all the races or against women,” she said. “Or there are people who think that because we have conservative values and we value the family and I value submitting to my husband, I must be against women’s rights.”

Her voice grew strong. “I would say it takes a stronger woman to submit to a man than to want to rule over him. And I would argue that point to the death,” she said.

She felt freer as she spoke. “Mike Pence is a wonderful gentleman,” she said. “This is probably a very bad analogy, but I’d say he is like the very supportive, submissive wife to Trump. He does the hard work, and the husband gets the glory.”

She turned to her husband. “Let’s be real, Micah, do you have any clue what goes on in our children’s lives on a daily basis? No.” They laughed.

“Pence you can picture as your father, as your dad,” he said.

But Mr. Biden as president really worried her: “Biden is a few fries short of a Happy Meal.”

‘They’re not Hispanic’

Jesús Alvarado first came to the area a few months after Mr. Trump did, and he was busy, preparing to start a church. It would be the first Hispanic church in nearby Orange City — one of just a few emerging in the region.

He was commuting from an hour away, and had heard about the speech like most people did, when the sound bite hit the headlines. All he really remembered was thinking that Mr. Trump sounded like Hugo Chávez, the former Venezuelan strongman.

Twenty years ago, less than 3 percent of Sioux County was Hispanic. Now, that figure has nearly quadrupled, largely as the pork and dairy industries have relied on Hispanic workers.

Most Hispanic migrants who come to the area are Catholic, but many convert to evangelicalism, as he did, Mr. Alvarado said in his office at Nueva Esperanza Iglesia, or New Hope Church. They kept a low profile, especially the ones without the right papers. At first even he had trouble finding them. Mostly they seemed to stick to work, home and the grocery store.

“There’s fear in the people,” he said. “The fear, the fear of losing everything —” His unfinished sentence hung in the air. The lights in the main fellowship hall were off.

Mr. Alvarado, 64, remembered how he ran away from home in Mexico when he was 13. His mother had died when he was an infant, he said, and his aunt and uncle could not pay for him to get an education. He found agricultural work wherever he could, in New Mexico, California, Texas, Colorado. At the time, he was undocumented. He met his wife when they were both being detained on a bus. She was dressed for a dance, he remembered, and three days later, on Valentine’s Day, they got married.

When he was detained another time, he said, a Hispanic pastor spoke to the judge on his behalf, reducing his sentence. He prayed on the side of the road and devoted his life to God, and eventually got U.S. citizenship. He began to start churches — this one was his sixth.

He and his wife were renting a farmhouse and taking care of four of their 13 grandchildren. He thought of how wonderful it was to raise them here. The whole community — the schools, the businesses — is evangelical-minded, he said, and the attitude toward immigrants has grown more welcoming. One of his church members had called it “a piece of heaven for us.”

He appreciated that Mr. Trump defended Christians. But he had another conviction: “We should welcome foreigners, immigrants.”

“Doing things like dividing the family, I don’t think that is very Christian,” he said. “And building walls, instead of helping people with medicine, food, especially old people getting sick for not having enough income.”

He does not talk about Mr. Trump with the white Christians around him. His church has now joined an existing Anglo church, he said, under the leadership of its pastor. Mr. Alvarado leads a Spanish service on Sunday afternoons for about 70 people, after the Anglo congregation finishes its two morning services.

“Maybe they know, that they realize that he is kind of persecuting Hispanics, so they won’t talk very much about that in front of me. I won’t, the same thing, I won’t tell them my opinion,” he said.

He grew quiet when he thought of why he believed that the white evangelical community around him supported Mr. Trump. Then he spoke as if it were obvious.

“They’re not Hispanic,” he said. “They have not been living what we have been going through.”

“They have to make their own decisions. I understand their point of view,” he went on. “For them, the benefit is that he is pro-Christian. Which is one of the things I like about him.”

He shared their worry about the disappearance of Christian values in America, he said, and he was especially concerned about the future of religious freedom.

“Our freedom has been under attack, that’s the way I see it,” he said. “This country was based and built on God-fearful leaders, and changing that is going to change one of the reasons why this country started, and the thing that everybody loves about this country. A lot of people are coming here because of the freedom.”

He will not tell his congregation which candidate he will vote for. Politics, he said, is just not something they talk openly about.

The line to Lafayette

It is deep into summer now. The pandemic has killed 160,000 people nationwide. Thousands have taken to the streets to protest the police killings of Black people. In Sioux Center, where the Black population is less than 1 percent, feelings about Mr. Trump remain largely unchanged.

Only three people in the county are reported to have died of the coronavirus. There was an outbreak of cases at the pork processing plant. Churches have mostly reopened. The closest thing to a protest was a walk for justice in Orange City.

“People in my circles, you don’t really hear about racism, so I guess I don’t know too much about it,” Mr. Driesen said of the protests. “When I see the pictures, I thought they all should be at work, being productive citizens.”

“I still think he is going to blow Biden away,” he said of Mr. Trump.

Ms. Schouten remembered a song she taught her children, called “Jesus Loves the Little Children.” She quoted the lyrics, which have been sung in churches for generations but would be considered racially insensitive today: “Red and yellow, black and white, all are precious in his sight.”

“We are making this huge issue of white versus Black, Black Lives Matter. All lives matter,” she said. “There are more deaths from abortion than there are from corona, but we are not fighting that battle.”

“We are picking and choosing who matters and who doesn’t,” she said. “They say they are being picked on, when we are all being picked on in one shape or form.”

The Trump era has revealed the complete fusion of evangelical Christianity and conservative politics, even as white evangelical Christianity continues to decline as a share of the national population. There are some signs of fraying at the edges of the coalition, among some women and young people. If even a small fraction turns away from Mr. Trump, it could make the difference to his re-election.

But even if he loses in November, mainstream evangelical Christianity has made plain its deepest impulses and exposed where the majority of its believers pledge allegiance.

There is a straight line from that day at Dordt four years ago to a recent scene at a chapel in Washington, where armed officers tear-gassed peaceful protesters in Lafayette Square and shot them with rubber pellets. They were clearing the way for Mr. Trump to march from the White House to St. John’s Episcopal Church and hold up a Bible, a declaration of Christian power.

“We have the greatest country in the world,” he said. “We’re going to keep it nice and safe.”

It was another instantly infamous moment, covered by cable news and decried by Democrats as an unseemly photo op. But in Sioux Center, many evangelicals once again received a different message, one that echoed the words uttered by a long-shot presidential candidate in a sanctuary on a cold winter morning.

“To me it was like, that’s great. Trump is recognizing the Bible, we are one nation under God,” Mr. Schouten said. “He is willing to stand out there and take a picture of it for the country to see.”

He added: “Trump was standing up for Christianity.”