Rick Perlstein has established himself as the pre-eminent historian of modern conservatism. Starting in 2001, with Before the Storm: Barry Goldwater and the Unmaking of the American Consensus, and continuing on through Nixonland (2008) and The Invisible Bridge: The Fall of Nixon and the Rise of Reagan (2014), Perlstein has shown how the Republican Party became more and more aligned with a powerful conservative movement, moving both the party itself—and the country—to the right.

With the Iowa caucuses less than a week away, however, there are signs of a crisis in conservatism. Donald Trump leads in the polls in every early state, the Republican establishment is panicking over the rise of both Trump and Ted Cruz, and the ability of that same establishment to control the nominating process seems tenuous at best. Perlstein and I spoke over the phone about Trump’s fascist tendencies, the history of extremism in America politics, and whether the Republican Party can ever be put back together again. The conversation has been lightly edited and condensed.

Are you surprised that things seem to be turning up Trump?

I had a very interesting experience this summer. I remember exactly when it was. It was when I was reading an article by [Evan] Osnos in the New Yorker about Trump. He happened to be covering the white nationalist movement, basically neo-Nazis. Coincidentally, it was right when Donald Trump burst onto the scene, and he wrote about how these guys were embracing Trump, as they never had embraced any Republican candidate before. The feeling I got was that this was the first time in a very long time that I’ve read anything about the Republican Party that I couldn’t assimilate into my normal categories. That was a very uncanny and uncomfortable feeling for me. I realized that I had to go back to the drawing board and rethink what was going on. This is something that’s very new, very strange, and very hard to assimilate into what we thought we knew about how the Republican Party worked. ...