Max Boot is a senior fellow at the Council on Foreign Relations and one of the most prominent conservative foreign policy intellectuals in America. He has advised the John McCain and Mitt Romney campaigns on foreign affairs; he is currently advising the Marco Rubio campaign.

Boot resists the neoconservative label, which he says he considers vacuous, but he nonetheless is widely considered a leading thinker of a conservative foreign policy ideology that most people would identify as neoconservatism, and he is associated with top neoconservatives such as William Kristol and Eliot Cohen.

Yet if Donald Trump wins the nomination, this lifelong Republican would be willing to pull the lever for Hillary Clinton.

"I'm literally losing sleep over Donald Trump," Boot told me over the phone. "She would be vastly preferable to Trump."

He's hoping that he's not alone — even if it means splitting the party over a Trump nomination.

"I would hope that the party would fracture," he says, "if the nominee were a fascist demagogue like Donald Trump."

Boot's reaction speaks to just how anxious Republican elites are about Donald Trump — and how much of a threat he poses to the ideas that have been central to their worldview for decades, particularly on foreign policy.

What follows is a transcript of our conversation, edited for length and clarity.

Zack Beauchamp: If forced to choose, you said you'd vote for Clinton over Trump. Why?

Max Boot: I'm not wild about Hillary, and I think she has a lot of weaknesses. I would be much happier if Sen. Rubio became president, and I'm much more in agreement with him.

But at least Clinton is informed and serious on foreign policy issues.

What she basically espouses is a pretty mainstream view. Obama is on the left end of the [mainstream] consensus; he has not totally destroyed [America's] basic post–World War II international strategy. Hillary is a little bit to the right of Barack Obama, and she would probably do a better job than he has done.

I disagree with Hillary a lot less than I disagree with Donald Trump.

ZB: Is Trump really that bad, from the point of view of a conservative foreign policy thinker?

MB: I think that American power has diminished under Obama. But if Trump were to become president, we would look back on the Obama presidency as a golden age.

If you take seriously Donald Trump's crackpot proposals, if they were implemented, it would leave America impoverished and isolated. He would actually be far more dangerous than that: He has plainly shown that he does not have either the intellect or the character to be commander in chief.

I'm frankly terrified at the notion that somebody as bigoted and ignorant as Donald Trump could possibly wind up in command of the most powerful military force in the world.

ZB: Was there a moment during the campaign that just struck you? Where you realized, "This guy, he's way beyond anything we could accept?"

MB: Last summer, when he attacked John McCain. Here's this guy, Donald Trump, who was a draft dodger, attacking John McCain, one of our greatest war heroes, and saying he's not a hero. I thought, right there, that his candidacy would flame out.

Of course, as it trolled along, he kept putting out one proposal that's crazier than the next. I thought he couldn't top this crazy idea that we were going to build a wall and make Mexico pay for it; I thought he should have been disqualified from the beginning, when he called Mexican immigrants "rapists" and "murderers," which is the worst kind of xenophobic hate-mongering.

"Donald Trump would destroy American foreign policy"

Then he tops himself, in December, by saying we should stop all Muslims from coming to the United States. It's unbelievable religious bigotry that was denounced by every leading Republican.

But then every time he says something crazy, he seems to grow stronger.

I don't know what's going on. I think it's possible, in fact likely, that there's this vein of xenophobia, protectionism, racism, and other sentiments out there that mainstream candidates in both parties are not willing to appeal to. I don't think that accounts for a lot of his support, but it is a significant share of it.

ZB: In a recent Weekly Standard piece, you and co-author Benn Steil take aim at Trump's proposals on foreign policy specifically. You seem to say they're well beyond the pale, whereas Clinton's — while not your favorites — are at least acceptable.

MB: Since World War II, there's been (to some extent) a bipartisan consensus. Free trade, American global leadership, the need to work with democratic allies and defend them — that's been the bedrock of American foreign policy in the post-1945 world. It's been responsible for us winning the Cold War and the greatest expansion of freedom in human history.

That's something I think Hillary Clinton and Marco Rubio understand. It's clear that Donald Trump doesn't understand the first thing about it. In fact, Donald Trump would destroy American foreign policy and the international system as it's been built up since World War II.

Donald Trump does not have a serious foreign policy thought in his head. He has no ideas, he only has impulses — and those impulses change every 30 seconds.

"I would hope that the party would fracture if it nominated a fascist demagogue like Donald Trump"

He loves dictators. He praises Putin, he loved the Tiananmen Square crackdown, he praises Kim Jong-Un. He said Saddam Hussein was great because he killed terrorists, which is a hell of a way to characterize the hundreds of thousands of victims Saddam Hussein claimed.

At the same time, he saves his venom for democratic allies like South Korea, Japan, and Germany because he thinks they're freeloaders. That's because, as he's repeatedly said, he admires strength and leadership, and people like Putin have it.

I do think there's been a swing in the Republican Party against the perceived excesses of the George W. Bush administration. I don't think we should go around, necessarily, toppling every dictator in the world — but I also don't think embracing these murderous thugs is going to be the solution to our foreign policy problems. And I think Donald Trump is certainly prone to embracing [them].

ZB: There definitely is a long-running strand on the American right, the part of the party that supported people like Pat Buchanan, that's been critical of both mass immigration and American global leadership. The modern Republican foreign policy view emerged, at least in part, as a reaction to that line of thinking. Do you see Trump as of a piece with it?

MB: I think he is a descendant, basically, of Charles Lindbergh, Joe McCarthy, George Wallace — who was a Democrat, not a Republican — and Pat Buchanan.

He is a direct descendant of that intellectual lineage — if I may use the word "intellectual" in describing Donald Trump, who doesn't seem to have one serious thought in his empty head.

His impulses are derived from the same well that people like the America First Committee and Joe McCarthy tapped into, which is essentially a form of isolationism, xenophobia, and racism.

But it's also a kind of Jacksonian impulse; if anyone directly messes with us, we will bash their heads in, or, as Donald Trump puts it, "bomb the shit out of them." But short of that, we will not assert American leadership in the world, we will not work with American allies, we will try to otherwise hunker down behind our walls. And we will focus not on external enemies but internal enemies.

And all of those movements had internal enemies that they focused on. The America First movement, along with the Nazis, tended to see the Jews as the internal enemy. McCarthy tended to see this communist fifth column as the enemy. George Wallace saw African Americans and civil rights as the internal enemy. And Trump identifies Mexicans and Muslims as the internal enemy.

There are some very strong echoes of very dark periods in American history.

But the reason I'm literally losing sleep over Donald Trump is, if you think about all of those previous demagogues, not a single one of them was half as close to ultimate power as Donald Trump now is.

ZB: What about just a Trump victory in the primary? Obviously if he were president, he could enact his policy. But would just winning the primary be enough to change the nature of the GOP itself — maybe pull it toward these views?

MB: That's a good question. I don't know; I think we're in uncharted territory.

I would hope that a significant portion of Republicans would break with the party and refuse to endorse Trump. I think you saw that with [Sen.] Ben Sasse; he did just that, and I hope others would follow suit.

"Anyone who thinks about cuddling up to him should understand the kind of damage he's going to do to their reputation"

I would hope that the party would fracture if it nominated a fascist demagogue like Donald Trump. Because in this case, devotion to country is more important than devotion to party. And I think there would be some splintering, though I don't know to what extent.

I have no doubt that there would be a lot of Republicans, especially establishment Republicans, who would be happy to embrace Donald Trump in a very cynical way.

ZB: I was about to ask what you thought about Chris Christie's endorsement of Trump this weekend. When he was a primary candidate, Christie had taken a line much closer to Rubio's — and all of a sudden he's endorsing Trump.

MB: I think it's appalling. I had respect for Gov. Christie; I think he's shown himself to be utterly unprincipled. Just watching his interview with George Stephanopoulos on Sunday was staggering: He could not defend a single one of Donald Trump's major positions. So why the heck is he endorsing Donald Trump?

This election is really a test of character for Republicans, to see who's embracing Trump and who doesn't. I've been very proud of people like Mitt Romney and [Sen.] Tom Coburn who have come out strongly against Donald Trump and have made clear that they would not associate themselves with the bigotry and extremism that Donald Trump represents.

ZB: Do you know of anybody in the Republican foreign policy world who would be willing to line up behind Trump?

MB: I'm sure he'll have somebody. Power always attracts people.

But I don't think anybody I know will. Anyone who thinks about cuddling up to him should understand the kind of damage he's going to do to their reputation, for being associated with this fascist demagogue.

I don't think anybody wants to be seen in that light.