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Donald Trump’s vice presidential pick is J.D. Vance, a relative newcomer to politics and fierce critic-turned-champion of the former president.

“As Vice President, J.D. will continue to fight for our Constitution, stand with our Troops, and will do everything he can to help me MAKE AMERICA GREAT AGAIN,” Trump wrote in his social media announcement on Monday.

James David Vance, who is 39, is a Marine Corps veteran, author and former venture capitalist from Middletown, Ohio. He has represented the state in the U.S. Senate since January 2023.

The Yale Law School graduate and investment banker first rose to national prominence in 2016 with the publication of his memoir Hillbilly Elegy, a bestselling account of his upbringing — and the plight of the white working class — in Appalachia, plagued by poverty, abuse and addiction.

The book, which also faced its share of social and historical critiques, was adapted into a movie in 2020.

Vance went on to found “Our Ohio Renewal,” a since-shuttered nonprofit with focus areas including education and opioid addiction.

“The success of the book has given me the flexibility, but also I think the platform to talk about some of the issues that are most important to me,” Vance told NPR in December 2016.

The organization dissolved in less than two years. Next, Vance co-founded a venture capital firm headquartered in Cincinnati and aimed at funding startups in underserved cities.

Vance’s family

The father of three is married to his Yale Law classmate Usha Chilukuri Vance, who has previously clerked for Chief Justice John G. Roberts, Jr. of the U.S. Supreme Court, as well as Judge Brett Kavanaugh and Judge Amul Thapar.

If the Trump-Vance ticket prevails, Vance — who will turn 40 in August — would be one of the youngest vice presidents in U.S. history.

His time in the Senate

In 2021, after months of hinting at his political ambitions, Vance launched his bid for the U.S. Senate.

He won a crowded primary race in May 2022 with the help of a last-minute endorsement from Trump, of whom he had once been unabashedly critical.

Vance went on to win the general election and assume his seat in the Senate, where he has been a leading defender of Trump and many of his policies, including opposing abortion rights and aid to Ukraine, calling for stronger border policies and downplaying the effects of climate change.

If Trump wins the presidency, Vance would have to resign his seat in the U.S. Senate — leaving an open spot in Ohio. In that case, it would fall to Ohio Gov. Mike DeWine to appoint his successor.

Under Ohio law, the governor appoints the person to fill a vacancy in the U.S. Senate until the next election, which would be in November 2026.

His history on Trump

Vance made no secret of his dislike for then-candidate Trump while promoting his book in 2016, calling him such choice insults as “noxious,” “cultural heroin” and “might be America’s Hitler.”

In an August 2016 interview on NPR’s Fresh Air, Vance said he would either vote third party, “hold my nose and vote for Hillary Clinton” or “write in my dog because that’s about as good as it seems.”

“But I think that I’m going to vote third party because I can’t stomach Trump,” he added. “I think that he’s noxious and is leading the white working class to a very dark place.”

But Vance has dramatically changed his tune over the years, condemning his own criticisms as “stupid” on the campaign trail in 2022. Trump, who has called Vance a “genuine convert” to his cause, seemed to put that checkered history behind them when he endorsed Vance in the primary that year.

“Like some others, J.D. Vance may have said some not so great things about me in the past, but he gets it now, and I have seen that in spades,” Trump said. “He is our best chance for victory in what could be a very tough race.”

Vance has been a staunch defender of Trump during his time in the Senate, even showing up as a surrogate to the former president’s hush money trial in New York.

Vance even went so far as to blame the rhetoric of the Biden administration for Trump’s attempted assassination at a Pennsylvania rally over the weekend.

Vance, like Trump, denies 2020 election results

In Sen. J.D. Vance, former President Donald Trump has found a fellow election denier as his running mate — one who’s already sown seeds of doubt about the upcoming presidential election.

While running for the Senate in 2022, Vance said on the campaign trail that he thought the 2020 election was “stolen from Trump.” And earlier this year, Vance told ABC News he still questions the results of the 2020 election.

“Do I think there were problems in 2020? Yes, I do,” he told George Stephanopoulos in February.

Vance, who at the time was being floated as a potential vice presidential nominee, also said that President Joe Biden’s victory over Trump should not have been immediately certified.

“If I had been vice president, I would have told the states, like Pennsylvania, Georgia and so many others, that we needed to have multiple slates of electors and I think the U.S. Congress should have fought over it from there,” Vance said. “That is the legitimate way to deal with an election that a lot of folks, including me, think had a lot of problems in 2020. I think that’s what we should have done.”

Reaction to his nomination

The White House declined to comment on his tweet following Trump’s VP announcement on Monday. But the Biden campaign was quick to slam Vance in a lengthy statement highlighting his views on abortion, healthcare and January 6.

“Donald Trump picked J.D. Vance as his running mate because Vance will do what Mike Pence wouldn’t on January 6: bend over backwards to enable Trump and his extreme MAGA agenda, even if it means breaking the law and no matter the harm to the American people,” said chair Jen O’Malley Dillon.

Elements of this reporting originally appeared as part of NPR Network live coverage of the RNC.