WASHINGTON — Elizabeth Graves, an ardent supporter of President Trump, is not opposed to vaccines. She said she had taken flu shots and pneumonia shots and, having just turned 50, was interested in being vaccinated against shingles.

But Ms. Graves, a legal transcriptionist in Starkville, Miss., said she would not be taking a coronavirus vaccine — and the sight of Vice President Mike Pence rolling up his sleeve to get vaccinated on live television on Friday, she added, would not change her mind.

Lawrence Palmer, 51, a field service engineer in Boiling Springs, Pa., and Brandon Lofgren, 25, who works in his family’s trucking and construction business in rural Wisconsin, said they felt the same way. All are fans of Mr. Trump, and echoed Ms. Graves, who said she was “suspicious” of government and that Mr. Pence’s vaccination “doesn’t mean a thing to me.”

It is a paradox of the pandemic: Helping speed the development of a coronavirus vaccine may be one of Mr. Trump’s proudest accomplishments, but at least in the early stages of the vaccine rollout, there is evidence that a substantial number of his supporters say they do not want to get it.

Until the past week, their objections were largely hypothetical. But with a second vaccine about to become available in the United States — the Food and Drug Administration on Friday authorized emergency use of the vaccine developed by Moderna, a week after the version developed by Pfizer and BioNTech won the same approval — more people will confront the choice of getting inoculated or not. The authorization will clear the way for the shipment of 5.9 million doses over the weekend and tens of millions more in coming months, greatly expanding the reach of the vaccination campaign as the nation grapples with the uncontrolled spread of the disease.

For the most part, public opinion has been swinging in favor of vaccination. Seventy-one percent of Americans are willing to be vaccinated, up from 63 percent in September, according to a survey released this week by the Kaiser Family Foundation.

Still, the survey found that Republicans were the most likely to be hesitant, with 42 percent saying they would probably not or definitely not be vaccinated, as compared with 12 percent of Democrats.

Experts say that vaccine hesitancy may diminish over time if people see friends and relatives getting vaccinated without incident. Sheri Simms, 62, a retired businesswoman in Northeast Texas who describes herself as a “moderate conservative” supporter of the president, said that while she did not intend to get vaccinated now, that could change.

“As more information comes out, and things appear to work better, then I will weigh the risks of the vaccine against the risk of the coronavirus and make a judgment,” she said.

The “anti-vaxxer movement” is not new, and it typically cuts across political parties. But the coronavirus vaccine, developed against the backdrop of a bitterly fought presidential election and championed by an especially polarizing figure in Mr. Trump, has become especially associated with partisanship.

During the campaign, while Mr. Trump was promising a vaccine by Election Day, some Democrats expressed concern about whether safety would be sacrificed in the rush to deliver a vaccine in time to help the president at the polls.

Political leaders in both parties worked on Friday to dispel concerns about the vaccine.

Mr. Pence, who took the Pfizer vaccine on Friday in a ceremony at the Eisenhower Executive Office Building in Washington, was not the only prominent public official to get vaccinated. On Capitol Hill, congressional leaders including Speaker Nancy Pelosi, a Democrat, and Senator Mitch McConnell, the Republican leader, were also inoculated against Covid-19. President-elect Joseph R. Biden Jr. and his wife, Jill Biden, are to be vaccinated on Monday.

In any other era, Mr. Pence’s vaccination, administered by a technician from the Walter Reed National Military Medical Center in Bethesda, Md., in images beamed across the country, would have been a moment to bring the nation together. He took the shot in front of a giant blue poster declaring in white block letters: “SAFE and EFFECTIVE.”

His wife, Karen Pence, and Surgeon General Jerome Adams were also vaccinated.

“I didn’t feel a thing — well done,” the vice president said afterward, adding that he wanted to “assure the American people that while we cut red tape, we cut no corners.”

But Mr. Trump was notably absent. One reason for the partisan divide over vaccination, experts said, is the president himself. His repeated denigration of scientists and insistence that the pandemic is not a threat, they said, have contributed to a sense among his followers that the vaccine is either not safe or not worth taking.

“I just don’t feel there’s been enough research on it. I think it was sped up too fast,” said Mark Davis, 42, a disabled worker in Michigan. “You don’t even really know the side effects, what’s in it.”

Mr. Lofgren agreed. “The jury’s out on whether it’s going to work,” he said, despite studies showing that the Pfizer and Moderna vaccines were more than 94 percent effective.

Experts say that “herd immunity” — the point at which so many people are immune that the spread of a virus is diminished — can be achieved when roughly 75 percent of the population is vaccinated. While the Trump administration is rolling out a public relations campaign to encourage people to get vaccinated, the reluctance among even a minority of Republicans is deeply troubling to public health experts.

Mr. Trump has been quick to claim credit for the manufacturing and distribution of the vaccine. “Distribution to start immediately,” he said Friday on Twitter, a day after an F.D.A. expert advisory panel recommended approval of Moderna’s vaccine.

Although the president has recovered from Covid-19, he remains vulnerable to reinfection. Dr. Anthony S. Fauci, the government’s top infectious disease scientist, has recommended that Mr. Trump be vaccinated. But he has given no indication that he will actually do so, and he has said little, if anything, to encourage Americans to get vaccinated.

“We need him taking a proactive role,” said Matthew Motta, a political scientist at Oklahoma State University who studies politics and vaccine views, adding, “The single best person to convince you to change your mind about something is somebody who agrees with you, somebody who you trust on other issues.”

Mr. Trump’s own flirtations with vaccine skepticism are well known. He repeated the debunked theory that vaccines cause autism as far back as 2007, when he said he had slowed his son Barron’s vaccination schedule, and as recently as 2015 while first running for president.

“Trump helped re-energize the anti-vaccine movement,” said Dr. Peter Hotez, an expert on vaccines, “and now he wants to pivot and make this his greatest accomplishment.”

Some conservative news media outlets are reinforcing the skepticism, tapping into suspicion of government by raising questions about whether officials are leveling with the public about the risks of the vaccines.

Tucker Carlson, the Fox News commentator, railed on Thursday against the “corporate image campaign” promoting vaccination, suggesting incorrectly that isolated instances of allergic reactions to the vaccine were being censored.

In interviews, Trump supporters said they felt the pandemic had been blown out of proportion. Mr. Lofgren said several of his co-workers had recovered from Covid-19, “with really no more than just cold symptoms.” Mr. Palmer said that if he “had an issue with breathing or a heart issue or a lung issue,” he might consider it, but does not want to take a chance.

Conspiracy theories — including the notion that the virus was created by the Chinese and Democrats to hurt Mr. Trump politically, or that the vaccine contains a microchip allowing the government to track people — cropped up in several conversations. Ms. Graves, who has diabetes, a risk factor for Covid-19, and has a master’s degree in library science, said such thoughts were creating doubts in the back of her mind.

“There’s no, quote, evidence that there’s a microchip or that here’s something nefarious about the whole thing,” she said. “But I have a gut check about all of it, and the government pushing it, and they’re finding all these popular people to take the vaccine. And it’s weird, like why are we pushing it so hard?”