Jeff Flake, 57, served Arizona in the U.S. Senate from 2013 to 2019, and for six terms in the House of Representatives before that. He is a contributor at CBS News and lectures around the world.

You said, “Never has a party so quickly abandoned its principles as [the Republican Party] did in the campaign of 2016.” Where does that take the party?

Well, this is the topic that’s discussed a lot. Not publicly. [Laughs.] But privately, certainly. I don’t know anyone who thinks that this is the future of the party. This is a demographic cul-de-sac we’re in, if nothing else. Anger and resentment only go so far; you have to have a governing philosophy. I don’t know of any of my colleagues who really believe this is it. I just couldn’t support [Donald Trump] long before he started to run. The birtherism thing was just too much for me. And then it piled on. So, for me, it would have been just a complete 180-degree turn. And I’m not saying that hasn’t been the case for many of my colleagues.

Has that surprised you?

It has. I’ve been puzzled by the trade-off some have made. There are some who think: Well, we’re getting some good conservative policy, good conservative judges, tax and regulatory reform. But I know that everyone worries about what this does to the standing of the party, long term. For the most part, it’s just trying to just stay in office, so you can fight another day. Maybe outlast the president. And stay in his good graces, knowing full well that at any time the president can pick up a phone and generate a primary.

The other night it was painful to watch the rally in Arizona: the president onstage with virtually all of my Republican colleagues from Arizona — the governor on down, some of whom had been reluctant previously to be on a campaign stage with the president. But who have just completely and utterly thrown in. Total capitulation of the party to Trumpism.

In your book you called out former colleagues Newt Gingrich and Tom DeLay for promoting take-it-to-the-mat politics. In the Senate there’s a legacy of decorum and working with the other side that’s clearly deteriorating now. Some of your long-standing colleagues appear to have abandoned some of those principles. I’m thinking of Lindsey Graham and others. Do you think that they’ve gone down a path that we can’t get back from?

Lindsey never goes too far one way without the ability to come back. I love Lindsey. And I frankly think he will be back — and will be better for it. Returning to the kind of senator who recognizes what the Senate is all about. You have to reach across the aisle. I do think we'll go back to that. My problem with Newt and Tom, the way they practiced politics was if you could pass legislation with a bipartisan majority or with a thin majority of only Republicans, they would opt for the latter and use it in the election. And that's just not the type of politics that the country needs.

I mean, most of my colleagues aspired to do more when they came to the Senate than just pass the president's executive agenda. They want to legislate. And I think many of them would happily return to that if there's good leadership and the right behaviors modeled from the White House.

But aren’t they supposed to be the leadership?

Yeah, certainly. But we've seen that they follow behind [this] leader.

Growing up on a ranch in Arizona, you have views on immigration very different from most in your party. Does that bother you, and have you found those views more broadly held than you would have thought?

More broadly than I would like. In Arizona, we're already majority-minority in the K-12 system. So for young people who've grown up around minorities or had a different experience than a lot of us in my generation, they don't harbor, I think, some of the prejudices that people in my generation do. Having said that, the behavior that they see modeled by elected officials and the party, it's difficult for them. Millennials look at the nativist attitude that a lot of elected officials present, and also the failure to address climate change in a serious way. They've been walking away from the party for a while, but now millennials are in a dead sprint away. And that's the real concern. If we go to a second Trump term, then there's a real danger.

During the Kavanaugh hearings, there was that viral elevator moment: Two women were telling you their stories, and I think what probably struck a nerve most was the look on your face. How did you experience that moment, and did it change you at all?

Well, that came a few hours after the most restless night I’ve probably ever had. I, along with a number of my colleagues, were getting calls from close friends, relatives, extended family. Dr. [Christine Blasey] Ford’s allegations stirred something in them and caused them to share their own stories. And that was weighing on me. Then the elevator moment came. So I was very unsettled. I didn’t think that we Republicans had done due diligence. I just felt that we needed to do more. And the elevator moment was helpful to have the resolve to [call for an FBI investigation].

Did you feel like the investigation did what you hoped it would? There was certainly the allegation that it was a bit of a fig leaf.

I wish that it could have started earlier and gone longer. And been more thorough. But it was not insignificant. You can’t make those public or nobody would ever submit themselves to appointments or elected office, but I wish the country could have read it. They would have felt better about where we are.

So that was not, in your mind, a party-over-conscience vote?

No. I was leaving office in a couple of months. There would have been nothing more satisfying to me than to deny the president. Given his boorish and bullying behavior and remarks about Dr. Ford and whatnot, that would have been immensely satisfying. But it would have, I thought, set a precedent that would be dangerous in the long term if we had an allegation that was uncorroborated — that that, in and of itself, could sink a nomination. That’s territory that the Senate shouldn’t be in.

Which do you think would be better for the Republican Party, and maybe the country itself: a second term for Trump or a sound defeat in November?

Oh, a sound defeat, no doubt. Long term for the Republican Party, you bet. And for conservatism as well.

You would feel comfortable casting a vote for a Democrat?

Yeah. This won’t be the first time I’ve voted for a Democrat — though not for president [before]. Last time I voted for a third-party candidate. [Laughs.] But I will not vote for Donald Trump.

But, listen, we have a good system. The pendulum swings when one party takes it too far. We'll be ourselves again. So it's not a pox on all your houses. I'm not trying to burn the place down or anything else. I think we'll be back.

This interview has been edited and condensed. KK Ottesen’s most recent book is “Activist: Portraits of Courage.”