Here are the key moments from the first 2016 presidential debate between Hillary Clinton and Donald Trump on Sept. 26. NBC Nightly News anchor Lester Holt moderated the debate at Hofstra University in New York. (Sarah Parnass/The Washington Post)

Here are the key moments from the first 2016 presidential debate between Hillary Clinton and Donald Trump on Sept. 26. NBC Nightly News anchor Lester Holt moderated the debate at Hofstra University in New York. (Sarah Parnass/The Washington Post)

Donald Trump and Hillary Clinton clashed in unusually personal terms during a taboo-breaking first general-election presidential debate on Monday evening, with Clinton accusing Trump of pushing “racist lies” about President Obama’s birthplace, and Trump accusing Clinton of lacking the “stamina” to be president.

“She doesn’t have the look. She doesn’t have the stamina. I said she doesn’t have the stamina. I don’t believe she does have the stamina,” Trump said, when moderator Lester Holt asked him about a past comment that Clinton lacked a presidential “look.” “You have to be able to negotiate our trade deals …I don’t believe that Hillary has the stamina.”

Clinton responded that she had traveled to 112 countries as secretary of state, and negotiated trade deals and other agreements. If Trump did that, she said, “He can talk to me about stamina.”

Trump responded that “Hillary has experience. But it’s bad experience.”

Clinton also noted that Trump has called women “pigs, slobs and dogs.”

That was a fitting end to a debate in which Trump repeatedly interrupted both Clinton and Holt, and accused both of misrepresenting his past statements, even though they were often right. The GOP nominee brought a flavor of the rowdy Republican primary into the normally staid world of late-fall debates, with asides, eye-rolls and complaints about the way he had been treated by Clinton, onstage and off.

“It’s not nice,” Trump said at one point, referring to Clinton’s TV advertising against him. “And I don’t deserve that.”

Clinton seemed thrown off-guard at several moments, at one point letting out a “whoo!” of apparent surprise, after a Trump attack on her temperament.

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Trump and Clinton accused each other of not possessing the proper temperament to be president, with Trump saying Clinton is not being strong enough, and Clinton saying Trump is too easily taunted.

During a discussion of national security, Clinton criticized Trump for saying that U.S. Navy ships should open fire on Iranian boats that had taunted them in the Persian Gulf. She re-used a familiar line from earlier in this campaign: “His cavalier attitude about nuclear weapons is so deeply troubling.…A man who can be provoked by a tweet should not have their finger anywhere near the nuclear codes.”

“That one’s getting a little bit old,” Trump said,

“It’s a good one,” Clinton said.

Trump had accused Clinton, earlier, for going along with President Obama’s foreign policy – criticizing her, in particular, for the nuclear deal with Iran, which he said had empowered Iran to become a major power and U.S. adversary.

“We lose on everything,” Trump said, striking a theme that he hit a number of times, on subjects ranging from trade to debt to cyber-attacks to military rivalries.

Trump also criticized the NATO military alliance, repeating a charge that the U.S. allies in that alliance were not paying enough for the defense that the U.S. provides.

“The 28 countries in NATO, many of them aren’t paying their fair share. And that bothers me,” Trump said. When he made similar comments, weeks earlier, Trump was criticized for undermining the West’s primary military alliance.

Trump later got into a brief argument with Holt about the Iraq War, which Holt had said he supported just before it began.

“I did not support the war in Iraq. That is a mainstream media nonsense,” Trump said. “Wait a minute. I was against the war in Iraq. Just so you put it out.”

“The record does not show that,” Holt said.

“The record shows that I’m right,” Trump said. He downplayed a 2002 interview with radio host Howard Stern, in which Trump had said he supported the war before it began. “I said,very lightly, ‘I don’t know, maybe, who knows.’”

In another part of the debate, cyber-attacks on the Democratic National Committee, which revealed internal emails embarrassing to Democrat Hillary Clinton and her supporters.

“I don’t think anybody knows it was Russia that broke into the DNC. She says Russia, Russia, Russia,” Trump said. “It could also be somebody sitting on their bed, that weighs 400 pounds.”

Trump has been accused of being too friendly to Russian President Vladimir Putin.

Later, in the debate’s last half-hour, the two candidates sparred about the Iraq War, and about who was responsible for the rise of the Islamic State. Trump blamed President Obama, saying that the U.S. had withdrawn too many troops, too quickly, and had failed to “take the oil” out from under Islamic State strongholds in Iraq and Syria.

“Now they have the oil all over the place,” Trump said, including those territories and the Islamic State affiliates in Libya.

Earlier, Clinton accused her Trump of pushing a “racist lie” that President Obama was not born in the United States.

“It can’t be dismissed that easily. He has really started his political activity based on this racist lie that our first black president was not an American citizen. There was no absolutely no evidence for it. But he persisted, he persisted year after year,” Clinton said. She cited 1970s lawsuits, in which Trump was accused of discriminating against black tenants: “He has a long record of engaging in racist behavior.”

Trump claimed credit for pushing the false notion that Obama was not born in the United States, saying that “I think I did a good job.”

“Nobody was pressing it, nobody was caring much about it,” Trump said, when Holt asked why he had continued to support the “birther” theory, even after Obama had released his birth certificate from Hawaii. “But I was the one who got him to produce the birth certificate, and I think I did a good job.”

Holt had asked Trump what he would say to black voters, who were unhappy that Trump has persisted so long with the false notion.

Trump said earlier that African Americans and Hispanics in U.S. cities are “living in hell,” because the cities are so violent. He said he would restore “law and order,” in part by using the aggressive stop-and-frisk enforcement tactics once employed by the New York city police.

“Secretary Clinton doesn’t want to use a couple of words, and that’s law and order. We need law and order. If we don’t have it, we’re not going to have a country,” Trump said. “We need law and order in our country.”

Holt told Trump that stop-and-frisk tactics had been ruled unconstitutional, because it disproportionately targeted blacks and Hispanics.

“No, you’re wrong,” Trump said, blaming a judge who was biased against police, and blaming a New York City administration for giving up on the case. “The argument is that we have to take the guns away from these people…These are people that are bad people.”

Trump declined again to release his income-tax returns, offering two explanations – first, that his returns were under audit and second, that the returns would not be that revelatory anyway.

“You don’t learn that much from tax returns, that I can tell you,” the GOP nominee said, after Holt had questioned the first rationale, saying that the IRS would not prohibit the release of tax returns under audit.

That exchange came during a period in which Clinton sharply criticized Trump over his taxes, suggesting that perhaps Trump had not paid any income taxes in recent years.

“That means zero for troops, zero for vets, zero for schools and health,” Clinton said.

Trump did not seem to push back against that suggestion. At one point, when Clinton suggested that Trump should have paid more taxes to improve the country’s infrastructure.

“It would be squandered too, believe me,” Trump said.

Trump responded by saying that his business acumen was exactly what the country needs now: “We have a country that’s doing so badly, that’s being ripped off by every single county in the world. That’s the kind of thinking that our country needs.”

The debate turned unusually contentious even in its first half-hour, with Trump repeatedly interrupting Clinton, and Clinton telling Trump, “Donald, I know you live in your own reality.”

At one particularly unusual moment, about 25 minutes in, Trump attacked Clinton for posting her plan to fight the Islamic State on her website. That, he said, was not something that Gen. Douglas MacArthur – a leader of American forces in World War II and the Korean War – would have done.

“Well, at least I have a plan to fight ISIS,” Clinton said.

“You’re telling the enemy everything you want to do,” Trump said. He followed with a charge that was not true: “You have been fighting ISIS your entire adult life.” The Islamic State has not existed for the bulk of Clinton’s adult life

Trum frequently talked over Clinton’s responses. Later, Clinton said she felt that Trump had blamed her for things beyond her control.

“Why not?” Trump said.

Clinton, who was said to have prepared to deal with an unpredictable opponent, still seemed caught off guard: “Just join the debate by saying more crazy things,” she said, seeming to assemble a zinger one word at a time.

The debate began with Donald Trump bemoaning the state of the country, and Hillary Clinton bemoaning Donald Trump.

Trump, the GOP nominee, answered the first economics-focused questions of Monday night’s debate by saying that the U.S. was being hoodwinked and taken advantage of by Mexico, China and other countries. He talked about manufacturing jobs leaving the U.S., and promised – as he had in the primary – to impose penalties on companies that take jobs offshore.

“Our country’s in very deep trouble. We don’t know what we’re doing,” Trump said. Of countries like China, he said, “What they’re doing to us is a very, very sad thing.”

Clinton began her first answers with an appeal to common purpose, talking about her two-year-old granddaughter. But she quickly turned to attacks on Trump, saying that he had rooted for the housing-market collapse a little less than a decade ago (“That’s called business, by the way,” Trump interjected), and saying that Trump would raise the debt by offering huge tax cuts to high earners.

“I call it Trumped-up trickle down, because that’s what it would be,” Clinton said, referring back to the trickle-down economics model of the 1980s.

Robert Costa in New York, Anne Gearan in Hempstead, N.Y., and John Wagner in New York contributed to this report.