Eight years ago, in the lead-up to the 2016 presidential election, JD Vance was a bitter critic of Donald Trump.

Publicly, he called the Republican presidential candidate an “idiot” and said he was “reprehensible.” Privately, he compared him to Adolf Hitler.

But by the time the former president tapped Vance to be his running mate on Monday, the Ohio native had become one of Trump’s most ardent defenders, standing by his side even when other high-profile Republicans declined to do so.

James David Vance’s transformation—from self-described “never Trumper” to stalwart loyalist—makes him a relatively unusual figure in Trump’s inner circle.

Democrats and even some Republicans have questioned whether Vance, who wrote a bestselling memoir “Hillbilly Elegy” and is now a US senator from Ohio, is driven more by opportunism than ideology.

But Trump, who survived an assassination attempt at a Pennsylvania campaign rally on Saturday, and many of his advisers see his transformation as genuine.

They point out that Vance’s political beliefs—which mix isolationism with economic populism—dovetail with those of Trump, and put both men at odds with the old guard of the Republican Party, where foreign policy hawks and free market evangelists still hold sway.

Republican Senator John Barrasso of Wyoming, whom Vance has described as a mentor, told Reuters that Vance shifted his views on Trump because “he saw the successes that President Trump as president brought to the country.”

In particular, Vance’s vocal opposition to US aid for Ukraine in its war with Russia has delighted Trump’s most conservative allies, even as it has upset some Senate colleagues.

“He understands what Trump is running on and, unlike the rest of the Republican Party in Washington, agrees with it,” conservative commentator Tucker Carlson, a vocal Vance supporter, told Reuters.

Vance, 39, was born into an impoverished home in southern Ohio. His pick may help boost the Trump campaign’s Rust Belt bona fides in a race that will be determined by voters in a handful of battleground states, including nearby Pennsylvania and Michigan, though his conservative views may be a turn-off for moderate voters.

“To the extent that he can do anything for the ticket, it would be to recapture being the voice of the American dream,” said David Niven, an associate professor of politics at the University of Cincinnati who has worked as a speechwriter for two Democratic governors, referring to Vance’s rise from poverty to US senator and vice presidential candidate.

After serving in the Marine Corps, attending Yale Law School and working as a venture capitalist in San Francisco, Vance rose to national prominence thanks to his 2016 book “Hillbilly Elegy.” In that memoir, he explored the socioeconomic problems confronting his hometown and attempted to explain Trump’s popularity among impoverished white Americans to readers.

He was harshly critical of Trump, both publicly and privately, in 2016 and during the opening stages of his 2017-2021 term.

“I go back and forth between thinking Trump is a cynical asshole like Nixon who wouldn’t be that bad (and might even prove useful) or that he’s America’s Hitler,” he wrote privately to an associate on Facebook in 2016.

When his Hitler comment was first reported, in 2022, a spokesperson did not dispute it, but said it no longer represented Vance’s views.

By the time Vance ran for Senate in 2022, his demonstrations of loyalty—which included downplaying the January 6, 2021 attack on the US Capitol by Trump’s supporters—were sufficient to score the former president’s coveted endorsement. Trump’s support helped put him over the top in a competitive primary.

In media interviews, Vance has said there was no “Eureka” moment that changed his views on Trump. Rather, he gradually realised that his opposition to the former president was rooted in style rather than substance.

For instance, he agreed with Trump’s contentions that free trade had hollowed out middle America by crushing domestic manufacturing and that the nation’s leaders were too quick to get involved in foreign wars.

“I allowed myself to focus so much on the stylistic element of Trump that I completely ignored the way in which he substantively was offering something very different on foreign policy, on trade, on immigration,” Vance told the New York Times in June.

In the same interview, Vance said that he met Trump in 2021 and that the two grew closer during his Senate campaign.

Vance declined to be interviewed by Reuters for this article and his spokesperson declined to comment for it.

The Ohio senator’s detractors see his shift in views as a cynical ploy to ascend the ranks of Republican politics.

“What you see is some really profound opportunism,” said Niven, the politics professor.

One issue where his position appears to have converged with Trump is abortion.

Vance implied in a 2021 interview that victims of rape and incest should be required to carry pregnancies to term, and in November he described a vote by Ohioans to add the right to abortion care to the state’s constitution as a “gut punch.”

This year, he said he supports access to the abortion pill mifepristone, a view that Trump shares.