Maybe it’s the Arizona air. Something has to account for the state’s profusion of free-spirited politicians like John McCain, Barry Goldwater, Morris K. Udall and Bruce Babbitt. Now add another name to the list: the state’s junior Republican senator, Jeff Flake.

Flake, a small-government, pro-tolerance conservative, may be President Donald Trump’s No. 1 enemy among congressional Republicans. Unlike more than a few colleagues, he doesn’t reserve his complaints about the president’s outrageous behavior for private conversations. Flake refused to endorse Trump last year, and has continued to criticize his conduct.

Now he’s publishing a book, “Conscience of a Conservative,” which argues for a “return to principle” and against the politics of personal destruction. It’s a title borrowed from a book Goldwater published in 1960, four years before he lost a disastrous presidential bid to Lyndon Johnson that nevertheless paved the way for Ronald Reagan’s conservative takeover of the Republican Party. Flake used to run the Goldwater Institute think tank in Arizona.

The party’s abandonment of core principles, he argues, began well before Trump. He’s especially critical of former House Speaker Newt Gingrich, whose main talent, in his view, was for “self-promotion,” and of former House whip Tom DeLay, a practitioner of “petty politics and the raw exercise of power” with the sole objective of winning elections.

The Republican Party, Flake believes, then “took the road too often traveled — of venality and mendacity and political expediency.”

I chatted with Flake on Wednesday. Here’s a lightly edited transcript of the conversation.

Q: How do you explain the Republican triumph of Trump?

A: This has been a long time building. We forgot our principles, so I think when we held the majority in the House and the Senate and White House and we didn’t cut spending and limit government, and because we couldn’t argue that we were conservative, therefore then we had to delve into the wedge issues. And we got further into those issues and have never gotten out.

Q: Trump has made it clear that he wants to get rid of special counsel Robert Mueller, who’s running the investigation of his ties to Russia. If he does, what should or will Congress do?

A: I think Congress would move ahead with its own special prosecutor. I do. It may be Bob Mueller. You cannot allow the president to so discard institutions that have been really so instrumental. I just don’t think that Congress would stand for that.

Q: Apart from less spending and more limited government, what is Flake conservatism?

A: Well, it’s a game of addition and not subtraction. Where you simply don’t play to the base. Seek to expand your constituency. Things like immigration, we expand to appeal to a broader audience. I think the current effort is to drill harder down in the base and rile them up when we’re done. We’ve seen that work for a cycle, and I think it did last time. It worked in California with Prop 187, but it doesn’t work in the long term.

Q: Do you really think you can re-create any consensus for free trade when, as you write, there are winners and losers and the politicians appeal to the losers?

A: I think we have no choice. If we want to grow economically, if we want to keep the standard of living that we have, we have no choice. And I think we can, and that’s not to say that it won’t involve different government programs to help those who have been left behind. There are certainly people who are left behind, but it has to start with honesty, and it’s not honest to tell a bunch of coal miners that their industry is coming back for the foreseeable future.

Q: Health care: You don’t like Obamacare, but can Congress move in a bipartisan fashion to improve what you think is a very flawed system?

A: We have no choice. We’ve reached the limits of what we can do with one party, and there are some calls to double down and bring another vote up. But there’s no appetite for that. The parties are meeting. Lamar Alexander [the Tennessee Republican who heads the Senate Health Committee] has already indicated they’re going to sit down, and that’s the way it should be.

Q: Taxes: It looks like there will be tax cuts but not tax reform, a big deficit-busting measure. Is that the way forward for a conscientious conservative?

A: No. I’m an ardent supply-sider, but I recognize that some tax cuts are not stimulative. Some are, some aren’t.

Q: Is eliminating the estate tax?

A: I think you have to, have to recognize we’ve done pretty well with the estate tax in terms of reforms that we’ve done. It’s not enough of a revenue raiser to argue that that’s what’s going to sink us. As far as the stimulative value of it, I don’t know whether that stimulates that much more.

Q: Do you worry about the effect it will have on the deficit?

A: Yes. I’m concerned that we don’t take the deficit into account. But keep in mind we’ve got to have the economic growth. This anemic, under-2-percent is not going to cut it.

Q: Where will the Republican Party be in five years? Will Trump have changed American politics or be a passing phenomenon?

A: Well, I think to the extent that he goes back to traditional conservatism — and I think on trade there are signs that he is — if he doesn’t, if he continues down this populist route, then I think this will be like other populist movements in the past, forgotten. Because populism is not a government philosophy.

Q: Do you think the Republican Party then really would move closer to what you’re talking about?

A: Yes, I do. I think we’ll return to more traditional conservatism. Limited government, economic freedom, free trade, strong defense, American leadership around the world.

Q: With the social issues being less important? And without turning as much to wedge issues that have been a focus?

A: Yes. I don’t think we have the appetite to go back there. I hope we don’t. I hope we focus on the issues that we can agree with, moving on.

Al Hunt is a Bloomberg View columnist. He was executive editor of Bloomberg News. Before that, he was a reporter, bureau chief and executive Washington editor at the Wall Street Journal.