If anyone still thinks Donald Trump should be president after Monday night’s debate, I’d like to know the reasons. In the segment dealing with foreign policy, he revealed himself—not for the first time, but more plainly than usual—to have little grasp of what power, diplomacy, and recent events are all about. Hillary Clinton left a few gaps open as well, but the differences between the two could be measured in leagues, even light-years.

The first question was about cybersecurity and Russia’s hacks of the Democratic National Committee. Hillary Clinton said we needed to make it clear that we’re not going to let state actors go after our information, and that, while we don’t want to unleash the full extent our far superior cyber powers, we will if this sort of “probing” continues. Trump came to the defense of Vladimir Putin, as he strangely has on many occasions, saying, “I don’t think anybody knows it was Russia.” The hacker, he added, could have been China, some other country, or “somebody sitting on their bed who weighs 400 pounds.” (What is it with Trump and overweight people?) In fact, as his intelligence briefer could have told him (and perhaps did), there is no doubt that the hack came from Russia. Then Trump rambled, saying, “My 10-year-old son is so good with these computers, it’s unbelievable. The security aspect of this cyber is very tough. We are not doing the job we should be doing.” He also used the question as a chance to boast of his endorsement by lots of generals and admirals.

Neither candidate pointed out that the United States engages in a lot of cyberespionage as well, albeit not of the same type of espionage as Russia, China, and others. This is a contest that has been going on, though secretly, for decades.

Clinton spelled out her plan for defeating ISIS: recruiting Silicon Valley to block jihadist traffic online; intensifying air strikes; supporting Arab and Kurdish ground fighters; and launching an “intelligence surge” by promoting more cooperation among law-enforcement, intelligence agencies, and foreign intelligence. These are all good ideas, which the Obama administration has been pursuing very forcefully (if, in some cases, a little late). Trump put forth no plan, saying he didn’t want to tell ISIS what he would do.

In a follow-up, Clinton pointed out that the fight against ISIS depends on our allies in the Middle East, who have Muslim-majority populations, which Trump has alienated with his rhetoric. Trump dismissed her premise, saying, “We’ve been working with them for many years, and we have the greatest mess anyone has ever seen.” His alternative? He didn’t say.

Trump said the biggest mistake happened when Obama pulled out of Iraq, even telling the jihadists the date of the withdrawal. After we left, ISIS erupted. Clinton noted, correctly, that the pullout date was specified in the 2008 Status of Forces Agreement signed during George W. Bush’s presidency and that the Iraqi government would not allow any U.S. forces to remain after that date.

On NATO, Trump took credit, as he has in the past, for revitalizing the alliance. A while back, he said NATO was obsolete unless it helped us defeat terrorism—then, lo and behold, he read in the New York Times that NATO was creating a counterterrorism commission. “I think it’s in large part because of what I said,” he claimed. Clinton pointed out that, after the Sept. 11 attacks, all the NATO allies invoked Article 5—which says an attack on one member is an attack on all—and joined our war against al-Qaida and the Taliban in Afghanistan. She could also have pointed out that NATO issued specific “policy guidelines” on counterterrorism in 2012, well before Trump’s off-hand remark.

And once again Trump prevaricated on the war in Iraq. He insisted that he always opposed the invasion, but then admitted that, in a 2002 interview, Howard Stern asked him about the war and, as he put it, “I said, ‘I don’t know, maybe.’ ” But, he insisted, he came out strongly against the war in an Esquire interview “shortly after the war started, I think in ’04”—perhaps forgetting that the war started in March 2003.

Trump called the Iran nuclear deal “one of the worst deals ever made by any country in history,” which, even if the deal’s critics were right, betrays a stunning ignorance of history. Clinton pointed out that the deal puts a “cap” on Iran’s nuclear program (that’s an understatement, as it has actually forced Iran to dismantle almost the whole program) and added, “There’s no doubt we have other problems with Iran, but I’d rather deal with those other problems having put that lid on their nuclear program.”

Clinton didn’t answer Trump’s other claim about the deal—that it required us to pay Iran $150 billion—so I’ll do it: That payment (and it hasn’t been nearly that much) came from Iran’s assets, which the United States and the European Union had frozen, as a sanction against its nuclear program. That was the deal: If Iran dismantles its nuclear program, the United States and the EU would unfreeze Iran’s assets; that’s what motivated Iran to make the deal.

The moderator, NBC anchor Lester Holt, asked whether the United States should adopt a “no–first-use” policy on nuclear weapons. This may have been the first time Trump had heard the phrase. First he said, “I certainly would not do first-strike; once the nuclear alternative happens, it’s over”—an interesting comment that many doves might welcome—but then he said, in his next sentence, “At the same time, I can’t take anything off the table.” But that’s what a no–first-use policy would do—explicitly take the nuclear option off the table. A quite detailed debate on this issue has been occupying the strategic community for decades, with legitimate points on both sides. It’s not surprising that a real-estate tycoon is unfamiliar with the debate, but you’d think someone might have briefed him on it.

Clinton dealt with the question the way presidents generally do: “Words matter when you run for president, and they really matter when you are president. I want to assure our allies, in Japan and South Korea and elsewhere, that we have mutual defense treaties, and we will honor them.” This, in response to Trump’s point, famously made in a New York Times interview, that he might not come to the defense of an invaded ally if the ally hadn’t paid its fair share—and that maybe it’s not such a bad thing if such remarks compelled Japan and South Korea to build their own nuclear weapons.

Finally, Holt asked Trump what he meant when he said Clinton didn’t have the “look” to be president. Trump replied, “She doesn’t have the look, she doesn’t have the stamina”—to which Clinton said, “As soon as he travels to 112 countries and negotiates a peace treaty, a cease-fire … or even spends 11 hours testifying in front of a congressional committee, he can talk to me about stamina.”

Game to Clinton.

Read more Slate coverage of the 2016 campaign.