Much has been made of the political pirouette J.D. Vance executed to secure the embrace of Donald J. Trump, a man he once called “cultural heroin” before seeking his endorsement for the Senate and, Wednesday night, accepting the Republican nomination to be his vice president.

Old friends and former classmates have expressed bewilderment at the seemingly irreconcilable versions of Mr. Vance. But contradiction has been central to Mr. Vance’s biography, nowhere more so than in his popular 2016 book, “Hillbilly Elegy: A Memoir of a Family and Culture in Crisis.”

The memoir, whose political dividends have far exceeded the millions of dollars it has paid in royalties and movie rights, emerged at a pivotal point in national politics, quickly becoming a go-to guide to the white underclass discontent that propelled Mr. Trump’s surprise presidential victory.

Mr. Vance used his personal account of overcoming dysfunctional Appalachian family values to tell a larger story about forgotten Americans. In his acceptance speech at the Republican National Convention in Milwaukee, he leaned again into those themes, at one point drawing attention to his mother, “who struggled with money and addiction but never gave up.” She stood in the audience when he continued, “And I’m proud to say that tonight my mom is here, 10 years clean and sober.”

But during Mr. Trump’s presidency, reaction to the book, like so much else in culture and politics, became increasingly polarized. While he expected pushback, Mr. Vance was confused by the attacks from opposite ends of the ideological spectrum, he professed in an afterword appended to the book in 2018.

“I’ve heard, for instance, from someone on the Left that my book is a victim-blaming piece of anti-government libertarianism,” he wrote, adding that “someone on the Right” had complained that the book’s premise “would justify a massive expansion of government welfare programs.”