The Senate candidate was a rising Republican when he abandoned his moderate roots. Now, those who have watched his transformation wonder if his rhetoric reflects who he really is.BEACHWOOD, Ohio — In the fall of 2016, Donald J. Trump’s presidential campaign was pressing Ohio’s young state treasurer, Josh Mandel, to step it up. A former Marine, he held some sway with Republican voters, and Trump aides wanted him doing more public events.But Mr. Mandel couldn’t quite find the time. He just had so many scheduling conflicts, he joked over breakfast with Matt Cox, a Republican lobbyist and, at the time, a friend. Mr. Cox recalled Mr. Mandel rattling off the excuses he used to avoid being too closely linked to a candidate he wasn’t sold on: Running after his three children, other political commitments, his observance of all those Jewish holidays.Once Mr. Trump won, any reluctance from Mr. Mandel fell away fast. Within weeks, he spoke at the president-elect’s first victory rally, slamming those who were “avoiding Trump” during the election. Five days after the rally, he launched his second bid for Senate, borrowing Mr. Trump’s catchphrases of a “rigged system” and “drain the swamp” for his announcement video.Mr. Mandel has not looked back. As he runs for the U.S. Senate in Ohio, the 44-year-old politician has become one of the nation’s most strident crusaders for Trumpism, melding conspiracy theories and white grievance politics to amass a following that has made him a leading contender for the G.O.P. nomination in this Republican-leaning state.His political evolution — from a son of suburban Cleveland to warrior for the Make America Great Again movement — isn’t unique. Across the country, rising stars of the pre-Trump era have shed the traditional Republicanism of their past to follow Mr. Trump’s far-right brand of politics, cementing the former president’s influence over the next generation of the party’s leaders.Mr. Mandel with a supporter at the Faith and Freedom Rally in Troy, Ohio, last month.Maddie McGarvey for The New York TimesBut Mr. Mandel’s transformation has been particularly striking. Friends, strategists and supporters who powered his start in public life say that Mr. Mandel has so thoroughly rejected his political roots in Cleveland’s liberal-leaning suburbs that he is nearly unrecognizable to them. Some are convinced that his shift began as a clear political calculation — following his party to the right. But with his recent entrenchment on the fringe, many now wonder if it is not just Mr. Mandel’s public identity that has changed, but also his beliefs.“He’s twisting himself into something he wasn’t, just to win an election.” said Mr. Cox, who is not a Trump supporter and has donated to Mr. Mandel’s opponents. “Telling obvious lies,” he said, “is not part of the game. It’s intentional. And you have to believe that, if you say it that often.”Mr. Mandel has burned protective masks and blamed the “deep state” for the pandemic and has claimed that former President Barack Obama runs the current White House. He has rejected the separation of church and state and said that he wants to “shut down government schools and put schools in churches and synagogues.” The grandson of Holocaust survivors who were aided by resettlement organizations, he has compared a federal vaccine-or-testing mandate to the actions of the Gestapo, and today’s Afghan refugees to “alligators.”And he denies that President Biden was legitimately elected. “He is my president,” Mr. Mandel said recently in a video, pointing to a Trump sign in an Ohio cornfield.How Donald J. Trump Still LoomsGrip on G.O.P.: Mr. Trump remains the most powerful figure in the Republican Party. However, there are signs his control is loosening.Power Struggle: Led by Senator Mitch McConnell, a band of anti-Trump Republicans is maneuvering to thwart the ex-president.Midterms Effect: Mr. Trump has become a party kingmaker, but his involvement in state races worries many Republicans.Post-Presidency Profits: Mr. Trump is melding business with politics, capitalizing for personal gain.Just the Beginning: For many Trump supporters who marched on Jan. 6, the day was not a disgraced insurrection but the start of a movement.“I want to believe that this is a character he is playing,” said Rob Zimmerman, a Democrat and former city councilman from Shaker Heights, Ohio. Mr. Zimmerman spent hours advising and fund-raising for Mr. Mandel, viewing him as a politician who could bridge partisan divides. “It is jaw-droppingly different. The Josh Mandel of 2003 — of 2016, even — would not recognize the Josh Mandel of 2021.”“This,” Mr. Zimmerman added, “has broken my heart.”Since launching this campaign, his third for the Senate, Mr. Mandel has largely spoken through conservative media outlets and his active Twitter account.Dustin Franz for The New York TimesMr. Mandel declined to be interviewed for this article. Since launching this campaign, his third for the Senate, he has largely spoken through conservative media outlets and his active Twitter feed, which was restricted last year for violating the platform’s rules on “hateful conduct.” (Mr. Mandel created a poll asking which “illegals” — either “Muslim Terrorists” or “Mexican Gangbangers” — would commit more crimes.)When a reporter for The New York Times attended a campaign event on Jan. 25 at a church in Troy, Ohio, Mr. Mandel singled him out and denounced the newspaper in Trump-like terms, calling it “the enemy of the people” and “evil.”Elsewhere, Mr. Mandel has disputed that his politics have changed, arguing instead that he is in sync with the people he hopes to represent. “The voters in Ohio in the past two presidential elections have made it very clear, they don’t want a moderate running Ohio or running America,” he told a local cable news station after announcing his candidacy last year. “I’m the opposite of a moderate.”Other Republicans challenge Mr. Mandel’s assessment of what most Ohio voters want. Brad Kastan, a Republican donor who has known Mr. Mandel for two decades, said he worried that the candidate was “painting himself into a corner so far out that he can’t win” in a general election.In a state that has moved to the right, backing Mr. Trump by eight percentage points in 2020, Mr. Mandel has been polling ahead of his primary rivals, including Jane Timken, a former head of the Ohio Republican Party, and J.D. Vance, an author made famous by his memoir “Hillbilly Elegy.” Much of the primary has revolved around winning Mr. Trump’s endorsement.Last spring, when summoned along with other candidates to Mar-a-Lago to jockey for Mr. Trump’s support, Mr. Mandel promised to hold nothing back to win the seat, according to a person with knowledge of the meeting who asked for anonymity to reveal a private conversation.Mr. Mandel’s stridency has surprised some in Beachwood, an affluent, predominantly Democratic suburb dotted with synagogues, where Mr. Mandel was a quarterback for his high school football team and then married into a wealthy Cleveland family.Mr. Mandel showed an early talent for standing out in a crowd at Ohio State, where he erected a 30-foot inflatable King Kong on the campus green to draw attention to his run for student government and won the presidency, twice.Shortly after graduating from the School of Law at Case Western Reserve, he won a City Council seat in Lyndhurst, a Cleveland suburb, drawing on support from his tight-knit community. When Albert Ratner, a major real estate developer and Ohio power broker, hosted a fund-raiser for Mr. Mandel, the candidate made a point of downplaying his Republican affiliation: “I really don’t care about partisanship,” he said, according to several people who recounted the gathering.Mr. Mandel attended just one City Council meeting before deploying to Iraq as an intelligence specialist in the Marine Corps Reserve. On his return trip home, his re-entry into U.S. airspace was announced at a high school football game to a cheering crowd.Mr. Mandel played quarterback for Beachwood High School’s football team and served in Iraq with the Marine Reserve Corps.Dustin Franz for The New York TimesAt 29, he won a seat in the Ohio Legislature, where he showed a keen understanding of the conservative causes that energized party activists. At one point, he took on the State House speaker, a fellow Republican, over a policy requiring ministers who led prayers in the chamber to submit their remarks in advance. The rationale was to avoid proselytizing in the Legislature. Mr. Mandel declared it an affront to religious liberty.“You know who fought the battle for our religious freedom? A 28-year-old Jewish guy,” said Lori Viars, an abortion-rights opponent who supports Mr. Mandel’s Senate bid. “I was so pleased to see him standing up when really no others did.”Running for state treasurer in 2010, Mr. Mandel was accused of trafficking in Muslim stereotypes after a campaign ad falsely implied that Kevin Boyce, the Democratic incumbent and Black man, was a Muslim.But Mr. Mandel’s reaction to the criticism cuts a contrast with the “fighter” image that he projects today. His campaign pulled the ad and he expressed regret, both publicly and privately to Mr. Boyce.“I think he had a sense of what’s right and what’s wrong, and I think he knew that wasn’t a right ad,” said Mr. Boyce, whom Mr. Mandel defeated. “He had a very strong reputation then as a moderate Republican and he seemed a little more reasonable.”Mr. Mandel had pledged to serve a full four-year term as treasurer. But he took the first steps toward a Senate campaign just five months after winning the job.He won the 2012 primary by courting Tea Party activists, but ran in the general election against Senator Sherrod Brown, the incumbent Democrat, as a business-friendly Republican. Campaigning that year for Mitt Romney, the G.O.P. presidential nominee, Mr. Mandel said he believed that Ohio voters rejected “hyperpartisanship” and wanted leaders who would “rise above it all to do the right thing.”(Mr. Mandel’s appraisal of Mr. Romney, now a senator and Trump critic, has curdled. “Mitt Romney is a loser,” he said last year.)Mr. Mandel had initially endorsed Marco Rubio in the 2016 presidential race, but he later backed Donald J. Trump. Andrew Harnik/Associated PressMr. Mandel’s sharpest political pivot came after the 2016 presidential race. He had endorsed Marco Rubio, then fell in behind Mr. Trump after he captured the nomination, though he privately expressed doubts about Mr. Trump’s credibility and business acumen and sometimes gave excuses when asked to stump for him, according to friends and former Trump campaign aides.After the October release of the “Access Hollywood” tape, in which Mr. Trump was heard making vulgar comments about women, Mr. Mandel condemned the remarks but affirmed his support for Trump, saying he would be better than Democrats on issues like gun rights, religious liberty and the Supreme Court.Within weeks after Mr. Trump’s victory, Mr. Mandel was matching Mr. Trump in rhetoric and tone.At the postelection Trump rally in Cincinnati, he said Ohio’s cities would become so-called sanctuary cities “over my dead body,” over chants of “Build the wall!”Today, he calls himself Mr. Trump’s “number one ally” in Ohio.Mr. Mandel’s second Senate campaign ended in his withdrawal from the race in January 2018, citing his wife’s health. The two later divorced. The Cincinnati Enquirer is suing to unseal his divorce records. A campaign worker now involved in a relationship with Mr. Mandel has been cited in local news reports as having driven other employees to quit.In Beachwood, discussions of Mr. Mandel’s politics can be as emotionally intense as a family feud. More than a dozen people approached in the affluent suburb declined to be interviewed, some saying they did not want to have to avert their eyes when they saw his relatives at the local coffee shop or the Beechmont Country Club.Some friends and former supporters said that in more recent encounters with Mr. Mandel they had searched for signs of the young man they once supported or even pleaded with him to cease his drift into far-right-wing politics.The criticism, they said, didn’t seem to register.“He made the decision that ‘My path here is to be all-in on Trump,’” said Alan Melamed, a Democratic political consultant who first met Mr. Mandel decades ago. “Since then, he has been going down the path of ‘How far to the right can I go, and how outrageous can I be?’”“People can change,” Mr. Melamed added. “And he did.”Mr. Mandel denies that President Biden was legitimately elected, and has referred to Trump as his president.Maddie McGarvey for The New York TimesKevin Williams More