The second presidential debate between Hillary Clinton and Donald Trump proved to be a grim, unsettling 90 minutes for America. Here are the three moments everyone will be talking about.

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1. Trump said that if he were president, Clinton would be "in jail." And if elected, he promised to open another investigation into her private email server.

The most important moment of the night came early on when Trump said that Clinton belonged in jail for her use of a private email server while serving as secretary of state, and he promised to appoint a special prosecutor to investigate her should he become president. It's worth noting that the FBI investigated Clinton's email server and concluded that, despite being "extremely careless," there was no evidence that Clinton or her staff intended to break the law.

"If I win, I am going to instruct my attorney general to get a special prosecutor to look into your situation,” Trump said. "Because there has never been so many lies, so much deception, there has never been anything like it."

Trump's threat to put Clinton in jail might seem normal now — there have been chants of "lock her up" at Trump rallies and even the Republican National Convention — but it shouldn't feel normal. In fact, it's unprecedented in modern American politics.

By invoking the threat of criminal charges against his opponent, Trump is breaking a long-established norm in American politics that the criminal justice system should not be used by one political party to exact revenge on another. Of course, we've always had witch hunts, legitimate congressional investigations, and even a couple of impeachments. But we've never really seen a presidential candidate say that if he wins, he's going to throw the loser in prison. (In fact, if anything, presidents have been criticized for taking it too easy on their counterparts, such as President Gerald Ford's pardon of President Richard Nixon or President Obama's decision not to investigate torture during the Bush administration.)

Here's why this is dangerous.

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This type of rhetoric can lead to violence, as was pointed out this summer by Yuval Rabin, the son of assassinated Israeli Prime Minister Yitzhak Rabin. Rabin compared Trump's rhetoric to the rhetoric that he says led to his father's murder in 1995.

"Intentional or not, the Republican presidential nominee is removing confidence in the democratic form of governance," Rabin wrote. "If an election is seen as illegitimate, if those who supported a candidate are viewed as somehow lesser Americans, then it becomes acceptable — and even appropriate — to work outside the political system."

Trump took this to the next level at the second debate by telling a massive national audience that Clinton belonged behind bars. As Andrew Sullivan wrote, "This is what happens in a banana republic."

The scary result of Trump's behavior is that, should Clinton win, there will be people convinced that she is an illegitimate president who should be in jail. And to justify it, they can say, "Hey, the Republican nominee for president agrees with me! I can't be that crazy." That's dangerous.

2. Trump probably did well enough at the debate to maintain his base of support.

If you've ever been bored on a long drive and turned your AM dial to conservative talk radio, you might be familiar with a lot of Donald Trump's message tonight. He used the 90-minute debate to insult the Clintons — right to their faces — in a way that conservative talk radio callers have been begging a Republican to do for years.

While he didn't bring up the wilder stuff, such as the Vince Foster murder conspiracy or Hillary Clinton's alleged closeted lesbianism, Trump did hit a few items on the Clinton-hater wish list. In addition to the aforementioned threat to put Hillary Clinton in prison, he invoked President Bill Clinton's marital infidelities, even hosting three women at the debate who've accused Bill Clinton of sexual assault. (Hillary Clinton did not take the bait and refused to address her husband's sex scandals.)

Trump also attacked Hillary Clinton for defending an accused child rapist in a criminal trial. (He hosted the victim in that case at the debate as well.) The whole story is that Clinton was forced by a judge to handle the case, despite her protestations.

Finally, Trump mentioned Benghazi, the email scandal, and the fact that Clinton "has tremendous hate in her heart."

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The point of these attacks was not only to do the typical damage a candidate intends during a debate, but also to signal to the far-right Trump supporters that he's still with them. And not only that, he's been willing to do what no other Republican has dared since 1992, stick his finger in the face of a Clinton and read them the riot act.

Will this work with undecided voters? Doubtful. Will it keep Trump's base intact? Likely.

3. Trump did not do well enough to fix his reputation with anyone outside of his core supporters.

There are two types of people left supporting Donald Trump.

On one hand, you have dyed-in-the-wool conservatives who would rather roll the dice with Trump than see Hillary Clinton take the White House and appoint a fifth liberal to the Supreme Court, thereby swinging the court left for the first time in decades. They might be disgusted by Trump, but that disgust will never exceed their disgust with liberals.

The other type has been with The Donald from the beginning and not only are they not disgusted by Trump, they celebrate the things that disgust the rest of us. They see the controversy about Trump's sexually vulgar words as merely political correctness run amok.

Those people will not leave Trump after tonight.

The problem, though, is that Trump desperately needs to expand his support beyond those two groups. No matter what's happened in this election, Trump's numbers have barely nudged past the low 40s. Best estimates say that he must, at minimum, push into the mid-to-upper 40s to have any chance to win. That would require winning over some of the people in groups that have been against him most, such as women, people with college degrees, and minorities.

Nothing Donald Trump did tonight will help him with those groups:

Women.

Even before the leak of the 2005 "Access Hollywood" tape with Trump's lewd comments about women, there's been a huge gender gap in this race, with women far more likely to support Clinton than Trump. Trump's stunt at the debate, where he used four women from the Clintons' past as props, probably hurt his case with women. And he did not help himself by his propensity to loom behind Clinton during the debate, an image that made more than a few people uncomfortable:

People with college degrees.

Trump was also not very substantive and again demonstrated a, shall we say, less-than-polished understanding of a range of policy issues, including foreign policy. At one point, Trump broke out in a long, rambling description of U.S. military failings in Syria and Iraq. (He seriously sounded like a guy in a bar who's getting a little too excited explaining military tactics.) That answer also included both a public break from his running mate, Indiana Gov. Mike Pence, on whether the U.S. should bomb Syria, and also what sounded like praise of Syrian dictator Bashar al-Assad.

This type of incoherence is not appealing to college grads.

Minorities.

And on reaching out to black voters, Trump basically offered the same answer for which he was pilloried earlier in the campaign. He said that black people might as well vote for him since previous politicians have failed them. Not exactly a convincing argument, even ignoring that Trump was once accused of housing discrimination, recently questioned the innocence of the Central Park Five, and once launched a years-long media tour accusing the first black president of not being a U.S. citizen. The other issue here was that he again failed to see black voters outside the context of urban poverty:

Trump also gave a strange answer about Islamophobia — basically suggesting that Muslim Americans are not reporting terrorist activity in their communities.

“Muslims have to report the problems when they see them,” Trump said. “And you know there’s always a reason for everything. If they don’t do that, it’s a very difficult situation for our country.”

This response prompted Muslim Americans on twitter to respond with the hashtag #MuslimsReportStuff.

Not good for Trump.

Now what?

So, no, Trump did not totally self-destruct tonight (as I predicted he would), but every hour he's not making up ground on Clinton is another hour she's closer to becoming the next president of the United States.

He's got one more shot in 10 days in Las Vegas at the final debate.

Update: Instant polls after the debate have Clinton as the winner, by a healthy margin. Here's what CNN's poll said:

The results showed a clear victory for Clinton, with 57% saying Clinton won, as opposed to 34% for Trump.