Neoconservatives have declared war on Donald Trump, releasing an open letter that says Trump would "use the authority of his office to act in ways that make America less safe, and which would diminish our standing in the world." But if you talk to them, this is grander than mere disagreement over the proper direction of US foreign policy.

The neoconservatives loathing of Trump is fundamentally about Trump's character: his vulgar authoritarianism and blustery disregard for basic democratic norms.

When I emailed Robert Kagan, a scholar at Brookings who had penned a blistering anti-Trump piece in the Washington Post, he didn't waste words.

"My column had nothing at all to do with foreign policy," Kagan told me. "It was strictly about stopping this would-be authoritarian from becoming president of the US."

In essence, they see Trump as an American version of the dictators they're so fond of toppling abroad. And they're ready to go to war with the organized Republican party, if necessary, to topple him.

Even if that means voting for one of their archenemies: Hillary Clinton.

Why neocons oppose Trump

On the surface, it seems obvious why neocons would oppose Trump. On virtually every foreign policy issue he's spoken about, he has attacked their policies:

Neocons counsel unyielding hostility to dictators; Trump says he'd "get along very well with Vladimir Putin."

Neocons endorse a more robust US intervention in Syria against dictator Bashar al-Assad; Trump wants to leave him in power.

Neocons support close US relationships with countries like South Korea and Israel; Trump wants to make allies pay the US for stationing troops there and pledges to take a "neutral" position on the Israel-Palestine conflict.

Trump has repeatedly labeled the Iraq war, the most famous neocon project, a disaster.

"Donald Trump does not have a serious foreign policy thought in his head," Max Boot, a senior fellow at the Council on Foreign Relations, told me. "He has no ideas, he only has impulses."

But in my conversations with several prominent neocons, it became clear that their reasons for detesting Trump go well beyond his mere policy statements. It's actually about Trump as a person; they fear that he is a kind of vulgar authoritarian — a "fascist demagogue," in Boot's words — who would do irreparable damage to the United States in office.

"Let me be clear: I think he'd be a disaster in the realm of foreign and national security policy," Eliot Cohen, a former Bush State Department official and one of the organizers of the anti-Trump petition, told me. "But there's just something profoundly outrageous about the guy. These latest things: David Duke, for God's sakes. The misogyny, the bullying, the lying, the advocacy of torture — it's appalling."

And while the open letter focuses on foreign policy specifics, it also takes shots at his character and commitment to basic democratic values. It calls him "fundamentally dishonest," and worries that he would pose "a distinct threat to civil liberty in the United States."

What this is, in essence, is an elitist backlash against authoritarian populism.

To be clear, I don't mean "elitist" pejoratively. Rather, I mean that the neoconservative establishment believes, deeply, that there is a mainstream consensus among American elites about what one can say and how one can act. They see Trump's approach to politics well outside the acceptable range, to the point that it poses a fundamental threat to American democracy.

Boot, for example, told the New York Times that "I would sooner vote for Josef Stalin than Donald Trump." It's an extraordinary statement from a member of a movement who claims toppling the Soviet Union as its principal accomplishment.

That's why he, Cohen, and Kagan would all vote for Clinton in a Clinton-Trump race. It's not, as some have suggested, that Clinton is ideologically simpatico with the neocons. Though Clinton is somewhat to the right of Obama on foreign policy, the neocons still view her pretty poorly.

Rather, it's that Trump is so dangerous that anyone inside the mainstream consensus — even someone they dislike as much as Hillary Clinton — would be a better choice.

"All I can say about Hillary Clinton," Cohen told me, "is that she'd be the lesser of two evils." He continued:

I could certainly never be enthusiastic about her. I think she's an extremely problematic figure in all kinds of ways. [But] I don't think she would be as damaging to us abroad. I don't trust her with the power of the federal government, but I trust Donald Trump even less.

For that reason, a number of prominent neocons who despise Trump — like the Weekly Standard's William Kristol or the American Enterprise Institute's Danielle Pletka — couldn't even bring themselves to vote in a Trump-Clinton general, and would instead support a third party candidate or just stay home.

"[W]hile I will never vote for a Democrat in wolf’s clothing like Trump, I will also never vote for a candidate as dishonest, as rapacious, as Hillary Clinton," Pletka told Politico's Michael Crowley in an email. "My vote is a precious thing."

The neocon war seems destined to fail

But some conservative foreign policy intellectuals don't hate Trump as much.

Take James Jay Carafano, the vice president for Foreign and Defense Policy Studies at the Heritage Foundation. As a top foreign policy manager at the most influential conservative think tank in America, Carafano is plugged into the conservative foreign policy world. Yet he wasn't willing to sign onto the anti-Trump petition.

"They sent it to me; we all all know each other," Carafano says of the letter. "I wouldn't even think about [signing] it."

Carafano has a number of reason for this position. For one, he believes it's "completely inappropriate" for him, as a policy intellectual, to be "telling the American public who is or is not acceptable to represent them."

But he also has met with members of Trump's campaign, and doesn't think that the candidate's views or character are especially alien to conservative ideals.

"From my experience of working with them," he explains, "I wouldn't write anybody off."

Interestingly, Carafano doesn't share the neoconservative ideological commitment to war on dictatorships. He opposed, for example, the wars in Libya and the proposed 2013 bombing campaign against Assad in Syria. His worldview is more centered on a basic commitment to strengthening the US military — and Trump has repeatedly promised to up defense spending considerably.

So Carafano, contra the neocons, thinks that Trump is preferable to Hillary Clinton. He writes off the candidate's more outlandish statements as mere campaign rhetoric.

"What Trump says on the campaign trail is stuff to keep Trump in the news; you know, mobilize the people he's trying to mobilize," Carafano says. "My assessment of Clinton's foreign policy is that there would be fair degree of continuity with Obama's foreign policy, and my candid assessment of Obama's foreign policies is that they generally don't work."

This illustrates a major problem for the neocon anti-Trump campaign. When people as prominent as Carafano are still refusing to rule out Trump, the move to excommunicate him is already failing.

Will neocons wage war on the Republican Party itself?

The staunch anti-Trumpers admit this, in their way. "I'm sure he'll have somebody," Boot says, "because power always attracts people."

The hope, instead, is to punish those anyone who appeases Trump. "Anyone who thinks about cuddling up to him should understand the kind of damage he's going to do to their reputation," Boot continued, "for being associated with this fascist demagogue."

But if Trump wins the nomination, this won't be possible. Trump will, quite literally, define the Republican Party until November. People who support him, or at least are willing to work with him, will be the ones shaping Republican doctrine.

This is why, if Trump wins the nomination, the neocons will have to wage war on the Republican Party itself. They do not think a party led by Trump could ever be one worth supporting because Trump is the one leading it. States run by dictators, in the neocon view, are enemies.

A Trump primary win "leaves the Republican party deeply and perhaps fatally wounded," Cohen says. He elaborates:

The damage that will have been done by the party, had it been willing to have as its candidate with senior official support, somebody who is that far away from supporting the basics norms of constitutional government — I think it would call into question the basic integrity of the Republican party.

What does war mean, in concrete terms? A party crackup, with the neocons and other like-minded factions trying to pull off Republican officials, donors, and organizers and get them to leave the party and oppose its nominee for president.

"I would hope that the party would fracture if it nominated a fascist demagogue like Donald Trump," Boot says. "I think there would be some splintering."

This is how fundamental a threat Trump is to the organized Republican Party. Neoconservatives are one of the three main ideological groups in the modern GOP, along with free-marketeers and social conservatives. That Trump is forcing them to contemplate secession — to support Hillary Clinton or maybe even form a third party — illustrates how his campaign is already smashing the party into tiny little bits.

Indeed, the neocons, if forced out, will become some of Trump's most relentless enemies. The idea of an authoritarian taking over the party they've called home isn't just a political cause; it's a personal insult, a spit in the face to everything they've committed their lives to.

"I understand their concerns," Carafano says. "These are people who have dedicated their lives to keeping the country safe and prosperous."

The pledge to oppose Trump, then, isn't merely a one-off event. It's more like the first bomb dropped in the invasion of Iraq. The question, as in Iraq, is if they're ready for what comes after.