(CNN) "American Carnage," Politico reporter Tim Alberta's deep dive into how President Donald Trump staged a hostile takeover of the Republican Party -- and what the party has done since -- is out today. Alberta's reporting in the book is already driving news cycles; former Speaker Paul Ryan's critical comments about Trump led to a series of tweets from the President attacking Ryan.

I reached out to Alberta to talk about the broader themes of his book, most importantly what Trump's rise tells us about the current state of the GOP -- and where it might head once he is gone. Our conversation, conducted via email and lightly edited for flow, is below.

Cillizza: Paul Ryan had plenty to say about Trump in your book. But he never made those critiques as speaker. Did he explain why not to you?

Alberta: In his own way, yes. His explanation boils down to the notion that President Trump is erratic, volatile and clueless about government -- and that without capable people around him to help steer the ship, it might just sink. Ryan was well aware that the Republican Party -- and his own reputation -- would suffer by virtue of remaining silent in the face of some of the President's indignities. But he was convinced that the greater risk was to the country itself. He believed that for as bad as things were, they would have been even worse if it weren't for people like him and John Kelly and James Mattis biting their tongues in order to preserve their influence over Trump, which they in turn used "to (keep) the guardrails up, to drive the car down the middle of the road, and don't let the car go off into the ditch.'"

Cillizza: How many current GOP members were willing to speak to you on the record about Trump? And how many did you ask?

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