Republican Sen. J.D. Vance of Ohio has begun to remind me of an old saying about Chicago weather: If you don’t like it, just wait a few minutes.

The same could be said—and some people do say it—about Sen. Vance’s big flip-flop from Trump critic to the reputed short list of possible Trump running mates.

When Sen. Vance arrived in the Senate last year, his fame preceded him along with a tantalizing dose of controversy.

The fame followed the popularity of his bestselling autobiography, “Hillbilly Elegy: A Memoir of a Family and Culture in Crisis,” as a sort of decoder for those of us who were struggling to understand Mr. Trump’s popularity among mostly white working-class voters in the 2016 presidential race.

Adding to the intrigue, Sen. Vance had built a reputation as a self-described “Never Trump guy” who mocked Donald Trump in interviews and since-deleted tweets calling Mr. Trump “loathsome,” an “idiot,” “noxious,” reprehensible and, my personal favorite, “cultural heroin.”

But all of that changed just 43 days before the 2022 Republican primary in Ohio, according to The New York Times, when a tweet from Donald Trump Jr., son of the former president, proclaimed, “Enough with the lies being told about this guy.”

Sen. Vance had turned from foe to a fan of the elder Trump,

Don Jr. assured his audience as Sen. Vance entered Ohio’s crowded field of candidates in the race to replace retiring Republican Sen. Rob Portman.

Sen. Vance also said he wasn’t worried about his chances to score the former president’s support. A month later, sure enough, the elder Trump confirmed his son’s sentiments by awarding his coveted endorsement to Sen. Vance, although not without some gratuitous barbs attached.

“J.D. is kissing my ass he wants my support so much,” the former president told a rally in Youngstown—while Sen. Vance, a Marine Corps veteran who served in Iraq, stood by.

In an interview with NBC News, Sen. Vance said at the time that while he believes Mr. Trump “gets a certain kick out of people kissing his ass,” he also thinks that the former president views those who do as “weak.”

By then, Team Vance was deleting his old negative tweets about the former president.

I had an additional reason to be interested in Sen. Vance and his book: He was born and raised mostly in Middletown, Ohio, the same economically troubled factory town where I grew up in more prosperous times a few decades earlier than Sen. Vance. His rags-to-riches Republican saga—and the politics-free movie it spawned starring Glenn Close and Amy Adams—took me on a mental journey back to my hometown, as seen from a side of town that had a lot fewer Black folks than my side.

The most memorable character, Sen. Vance’s grandmother “Mamaw,” well played by Close, reminded me of my own wise grandmother. But I also was struck by how fortunate I felt to have been born and raised in a two-parent household that, for all the struggles we faced, was not burdened by the problems of drugs and family dysfunction that plagued Sen. Vance’s upbringing.

Sen. Vance credits Mamaw with pushing him to put forth the effort that would improbably take him to a Yale law degree, service in the Marines and a lucrative career in corporate law, venture capital and now politics.

What to make of Sen. Vance now that he’s become among the most enthusiastic embracers of Trumpism? Why should anyone believe Sen. Vance when he said of Mr. Trump, “I think that he respects people who can defend themselves, who have their own ideas.”

No matter, I suppose, if you’re gunning to be vice president. “Having your own ideas” isn’t really in the job description.

It’s easy to see why Mr. Trump should consider Sen. Vance to be a strong contender. It’s quite a bit harder to see what the self-made Sen. Vance finds appealing in Mr. Trump, other than a means to a political end.

The writer is a columnist for the Chicago Tribune.