Donald Trump is not fit to lead the free world. He is a narcissistic, thin-skinned bully, a serial liar, a man who shows not the slightest respect for the office to which he aspires.

This shouldn't need saying, but it evidently does. For the past three weeks, in the media and online, conservative critics of Trump have been met by the response, "Oh, so you want Hillary, do you?"

Hang on. This isn't about Mrs. Clinton's shortcomings which, I agree, are also a disqualification. "Is Trump any worse than Hillary?" isn't just setting the bar absurdly low; it's also the wrong question. The right question is, "Is Donald Trump fit to be president?" And the answer must surely be, "No."

We are talking here of someone who makes things up so breezily that he is barely aware of what he is doing; someone who randomly accused an opponent's father of being involved with the assassination of President Kennedy; someone who seeks to have critical journalists removed from their posts; someone who tells his supporters to "beat the crap" out of hecklers.

Next to his moral unsuitability, the fact that he is bad news for conservatives seems almost trivial. It's not his big-government protectionism that ought to bar him from high office. It's not even the way in which he will undo decades of progress and taint the Republicans once again with xenophobia — this is a man who can't even bring himself consistently to disown the Klan, for Heaven's sake.

No, the real disqualification, from a conservative point of view, is Trump's refusal to recognize that he is aspiring to an office bigger than he is.

To remind you, when he was asked on Twitter by Sen. Ben Sasse of Nebraska: "Will you commit to rolling back Exec power & undoing Obama unilateral habit? These r sincere questions & I sincerely hope u answer rather than insult," Trump replied, "@BenSasse looks more like a gym rat than a U.S. Senator. How the hell did he ever get elected?"

"So you want Hillary, then?" For the last time, this isn't about Hillary. It's about defending the republic from a candidate who is hostile to its foundational values. There are 320 million U.S. citizens. I can't believe that it's impossible to find one who regards the presidency as more than a personal plaything.

The mechanics of how that might happen will be worked out by people who are much more involved than I am. It may be that the Republican Party as an institution must for now be regarded as conquered territory. After all, it has little choice but to follow its own rules.

The citizens of that territory may, as it were, sneak across the lines and enlist with allied armies. But its formal structures are now garrisoned by the enemy. Yes, enemy: Donald Trump is inimical to the core Republican values of personal freedom, limited government, enterprise and a patriotic foreign policy.

If the party itself is temporarily occupied, though, the same does not apply to the wider conservative movement. Perhaps another Republican will stand as an independent, or perhaps there will be a serious third-party challenge.

I've always had a soft spot for Gary Johnson, the deeply principled Libertarian, who twice won New Mexico as a Republican, and who vetoed more bills during his time in office than the other 49 state governors put together.

Still, as I say, it's not my call. There are people who are much closer to all this than I am.

I say only one thing with absolute certainty: Don't vote for an unfit candidate simply because you dislike another unfit candidate. Doing so makes you complicit. It means endorsing one of two amoral, power-hungry people who would very probably ignore their oath of office.

As Vaclav Havel used to say in Czechoslovakia, living under a Communist regime doesn't mean that you have to legitimize it. A citizen can still retain his or her integrity by refusing to vote for the approved list, refusing to display party posters, refusing to repeat official slogans. And integrity matters. Indeed, at present, it's pretty much all that American conservatives have left. For the love of God, cousins, don't throw it away.

Dan Hannan is a British Conservative MEP.