Senator J.D. Vance, the newly announced running mate to former president Donald Trump, has gone on a rapid journey over the past eight years from bestselling author and outspoken Trump critic to one of Trump’s staunchest defenders and, now, his would-be second-in-command.

Before running for office, Vance, 39, was known as the author of Hillbilly Elegy, a bestselling memoir recounting his upbringing in a poor family that also served as a sort of sociological examination of white working-class Americans. The book was published the summer before Trump’s election in 2016, and many readers looked to it after his victory as a sort of guide to understanding Trump’s support among white working-class communities.