Most folks who read the book presume that Vance is a liberal. He is, after all, an Ivy League (Yale) trained attorney working for an investment firm in San Francisco, and the bulk of the book focuses on the causes and consequences of poverty. Vance, however, is a conservative. Reflecting on this presumption shortly after speaking at a gathering in New York, Vance remarked in an interview with the Washington Post, "It’s very interesting, right? It seems to me an indictment of the Republican Party that if you talk about issues of poverty and upward mobility, people assume you’re a Democrat.” Vance is not a Trump fan, though, and did not vote for him in the election. He believes that Trump "ran an angry, very adversarial campaign that in tone matched the frustrations of the people I wrote about. He certainly ran a pretty cynical campaign, and got a lot of votes from people who are feeling cynical about the future."
It seems to me that for whatever reason (or rather reasons -- seldom can you reduce any phenomenon to a single factor), the Democratic party has lost touch with its working class base. I'm not sure what it needs to do to recapture it, but reading Hillbilly Elegy is probably as good a place to start as any.