LAUGHLINTOWN, Pa. — Michael Testa, 51, an Army veteran and handyman, drives a minivan plastered with stickers reading “Trump Won.”He recently stood in the rain and mud for hours to attend Donald Trump’s Pennsylvania rally. He calls himself a “conspiracy realist” and said he’s one of millions who believe the 2020 election was stolen from the former president.But as he sat on his front porch in Laughlintown, a small borough of Westmoreland County outside Pittsburgh that was once home to the Mellon family fortune, he was undecided about which candidate to vote for on Tuesday in Pennsylvania’s Republican primary for Senate. He has misgivings about supporting Mehmet Oz, the celebrity doctor Mr. Trump has endorsed.“I’m not going to be somebody who does something just because one person says so, even if that person is Trump,” Mr. Testa said.Like other Republican primaries throughout the country, the Pennsylvania Senate race is testing just how strong Mr. Trump’s grip remains on the party. But unlike other primaries this year, the Senate contest in Pennsylvania has suddenly pivoted into something else — a case study of whether the movement Mr. Trump created remains within his control.In interviews with more than two dozen Republican voters in western Pennsylvania, many echoed Mr. Testa’s ambivalence and uncertainty about Dr. Oz — despite Mr. Trump’s backing, they view him with suspicion, call him “too Hollywood” and question his ties to the state. Those Republicans, including Mr. Testa, said they were instead voting for or considering voting for Kathy Barnette, the far-right author and conservative-media commentator who has surged in the polls on a shoestring budget.In a race that could determine control of the Senate, many Republicans in the state find themselves deeply devoted to Mr. Trump yet, at the same time, less swayed by his guidance. Trumpism, as Ms. Barnette herself has put it on the campaign trail, is bigger than Trump.Many voters said they were choosing who they believed would carry out Mr. Trump’s ideals, even if they and the former president disagreed on who could best accomplish that. And interviews showed how effectively Ms. Barnette, who has never held public office, had used her life story as a poor, Black child of the South to connect with white working-class voters in western Pennsylvania. At events and in her ads, Ms. Barnette often invokes the phrase “I am you.”Many voters who said they planned to vote for Ms. Barnette struggled to remember her name and said they were supporting “that Black woman.” Those who said they were voting for her said they were unaware of or unbothered by her history of homophobic and anti-Muslim views. But her strong anti-abortion beliefs — Ms. Barnette calls herself a “byproduct of rape”— have been a key part of her appeal to white conservatives.Dolores Mrozinski, left, and her daughter, Janey Mrozinski, are drawn to Ms. Barnette.Jeff Swensen for The New York Times“I like what she stands for,” said Dolores Mrozinski, 83, who first watched Ms. Barnette on the Christian Television Network and was immediately impressed. “She’s no-nonsense and the real thing.”Understand the Pennsylvania Primary ElectionThe crucial swing state will hold its primary on May 17, with key races for a U.S. Senate seat and the governorship.Hard-Liners Gain: Republican voters appear to be rallying behind far-right candidates in two pivotal races, worrying both parties about what that could mean in November.G.O.P. Senate Race: Kathy Barnette, a conservative commentator, is making a surprise late surge against big-spending rivals, Dr. Mehmet Oz and David McCormick.Democratic Senate Race: Representative Conor Lamb had all the makings of a front-runner. It hasn’t worked out that way.Abortion Battleground: Pennsylvania is one of a handful of states where abortion access hangs in the balance with midterm elections this year.Electability Concerns: Starting with Pennsylvania, the coming weeks will offer a window into the mood of Democratic voters who are deeply worried about a challenging midterm campaign environment.Years ago, Ms. Mrozinski and her daughter, Janey Mrozinski, a 62-year-old physical therapist, watched Dr. Oz on television and even admired him. Now, the elder Ms. Mrozinski said, “he just doesn’t seem genuine.”“I don’t even know if he really lives in Pennsylvania,” she said, referring to Dr. Oz’s long history, until recent years, of living and voting in New Jersey. “He seems more Hollywood than here and it doesn’t impress me.”Her daughter added, “He looks like he had a face lift.” On the other hand, David McCormick, a former hedge fund executive who is also running in the primary, was simply, she said, “too much, too proud of himself.”In many ways, the vote for the Senate seat is as much a battle over the perception of authenticity as any ideological or policy debate. For months now, the leading candidates have each tried to align themselves closely with Mr. Trump and promote their conservative credentials. In the tight contest between the leading contenders — Dr. Oz, Ms. Barnette and Mr. McCormick — all three of them have tried hard to cast themselves as the true MAGA warrior.Some voters have clearly made up their minds about which one they believe is more authentic. But others are still deciding.One glance at John Artzberger’s auto body shop along Highway 8 in Butler County makes his political leanings clear: A “Let’s Go Brandon” flag flies from the shop’s marquee, and Trump paraphernalia covers a large wall near the entrance. When one customer asked him to place a Barnette lawn sign out front, he did not hesitate to agree. Still, the sign was just a sign — he said he was undecided and considering voting for either Ms. Barnette or Dr. Oz.John Artzberger, a body shop owner in Butler, Pa., said he was uncertain who would win his vote, Ms. Barnette or Dr. Oz.Jeff Swensen for The New York Times“She’s 100 percent on our side — close the border, pro-life,” Mr. Artzberger, 68, said of Ms. Barnette. “If she gets it, she’s going to be for the people.” Like many other Republicans in Butler County, Mr. Artzberger views Dr. Oz’s previous time in the spotlight with disdain.“But then again, Trump had been in the public eye, too, and he ended up being really with us,” he said. “I’ve changed, so maybe he changed, too.”In Laughlintown in Westmoreland County, it takes about 10 steps to travel from the front porch of Mr. Testa’s old Craftsman to the front doors of the small brick church next door. In that short distance lies a glimpse of the Republican Party’s identity crisis.Jonathan Huddleston, 48, the minister of Laughlintown Christian Church, calls himself a Never-Trump Republican but remains committed to the party to, in part, “help vote the wackos out.” He, too, is undecided — he is considering voting for Mr. McCormick, who tried but failed to win the Trump endorsement.Jonathan Huddleston, a minister in Laughlintown and a moderate Republican, is another undecided voter.Jeff Swensen for The New York Times“I want to support the Romneys of the world, the reasonable leaders, the ones who drew me to begin with,” Mr. Huddleston said. “Now I’m searching to find people like that. All of the other voices are drowning them out.”Some Republican voters said they had tried to tune out the deluge of attack ads on television from Mr. McCormick and Dr. Oz, who have each spent millions of dollars of their own wealth in the race. The backlash against the Oz and McCormick ads appeared to benefit Ms. Barnette, who has spent less than $200,000 in her campaign.Understand the 2022 Midterm ElectionsCard 1 of 6Why are these midterms so important? More