Daniel W. Drezner is a professor of international politics at the Fletcher School of Law and Diplomacy at Tufts University and a regular contributor to PostEverything.

Last night’s third presidential debate was the most substantive of the three (an admittedly super-low bar). Chris Wallace did an excellent job of moderating and made the wise tactical decision to open with policy questions before turning to both candidates’ scandals for a brief spell, and then pivoting back to policy. Donald Trump seemed to have prepped more for this debate than either of the first two, and occasionally got in some sharp attack lines on Hillary Clinton’s record.

And yet, nothing in the above paragraph matters, because on at least three separate occasions, Trump said something that made it pretty clear he is radically unfit to be the president of the United States. Let’s just list them here for posterity:

1) Refusing to say he would accept the election results if he lost. If you’re Donald Trump, or a Republican politician who has endorsed Donald Trump, this is not a good look for you:

I’m not going to belabor this point as it is clearly the story of the day and analyzing it, like almost all analysis of Trump, inevitably leads you to the same conclusion. But to give an example of how serious Trump’s breach of political norms was, let’s go to the Twitter feed of Richard Haass, president of the Council on Foreign Relations (CFR):

Haass is obligated by his position to be strictly nonpartisan on matters pertaining to presidential elections. Tweeting this is the CFR equivalent of saying that Trump has crossed waaaaaaay over the line with his statements.

2) Refusing to acknowledge the intelligence community’s consensus that Russia is responsible for hacking email accounts to interfere with this election. A joint DHS/ODNI statement makes the assessment of the intelligence community crystal clear. Trump was informed of this assessment as part of the intelligence briefings he receives as the GOP nominee. And yet this exchange took place last night:

CLINTON: I think that this is such an unprecedented situation. We’ve never had a foreign government trying to interfere in our election. We have 17 — 17 intelligence agencies, civilian and military, who have all concluded that these espionage attacks, these cyberattacks, come from the highest levels of the Kremlin and they are designed to influence our election. I find that deeply disturbing.

WALLACE: Secretary Clinton…

CLINTON: And I think it’s time you take a stand…

TRUMP: She has no idea whether it’s Russia, China, or anybody else.

CLINTON: I am not quoting myself.

TRUMP: She has no idea.

CLINTON: I am quoting 17…

TRUMP: Hillary, you have no idea.

CLINTON: … 17 intelligence — do you doubt 17 military and civilian…

TRUMP: And our country has no idea.

CLINTON: … agencies.

TRUMP: Yeah, I doubt it. I doubt it.

CLINTON: Well, he’d rather believe Vladimir Putin than the military and civilian intelligence professionals who are sworn to protect us.

Seriously, what the hell can you say about this? I get the idea that presidents should interrogate and question the intelligence community. I get guarding against groupthink. But this is Trump unilaterally asserting without any foundation whatsoever that he knows what he’s talking about and intelligence professionals don’t. In this section of the debate Trump combined the three worst aspects of his personality: his stupidity, his arrogance and his vanity. The only conclusion one can draw is that Trump refused to criticize Russia because he likes the fact that Vladimir Putin said nice things about him. And if that’s the way Trump makes decisions, he should be kept as far away from the Oval Office as possible.

And finally …

3) Refusing to act like a mature adult. The moment this debate turned was when Clinton dropped this line in response to an immigration question: “When it comes to the wall that Donald talks about building, he went to Mexico, he had a meeting with the Mexican president. Didn’t even raise it. He choked and then got into a Twitter war because the Mexican president said we’re not paying for that wall.”

Clinton was obviously baiting Trump with that line — and yet, the baiting obviously worked. The moment Clinton said the word “choked,” Trump’s eyes narrowed into slits. Whatever self-control he’d managed to muster in the opening sections melted away. He melted down on the Putin jab. He said to Clinton “You’re the puppet! No, you’re the puppet!” sounding even more immature than usual. He kept interrupting her. He even challenged moderator Chris Wallace a few times. And then, at the very end of the debate, came this moment:

What a sorry, immature specimen of a human being.

In the third debate, Trump vindicated Clinton’s strongest attack during the general election campaign: that Trump is temperamentally unfit to be president.

The instant debate polls suggested that Clinton won these debates, but that’s not really the important part. The important part is that Trump lost — bigly — the last chance he had to change the narrative of this election. And he also demonstrated why that’s probably the best outcome for everyone concerned.