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)

“She doesn’t have the stamina,” Donald Trump said of Hillary Clinton late in Monday’s presidential debate. He had been asked to explain his comment that Clinton lacked a “presidential look.” “I said she doesn’t have the stamina,” he went on. “And I don’t believe she does have the stamina. To be president of this country, you need tremendous stamina.”

But it was Trump, not Clinton, who was unable to last 90 minutes on Monday. Only one candidate made supporters more enthusiastic, an essential task in the run-up to Nov. 8.

During the debate, I followed a dial group of 100 likely voters set up by Women’s Voices Women Vote, Democracy Corps and Democratic pollster Stan Greenberg. Besides turning dials up or down during the debate to indicate their approval or disapproval, they also answered questions before and after the debate. After the debate, though there was only a small shift in the group toward Clinton, they had a much more favorable view toward her, and a number of voters who had come in as “weak” Clinton supporters left as “strong” Clinton supporters. Post-debate polls had similar findings: In CNN’s poll, 55 percent of Democrats and 61 percent of Clinton supporters said they were now more likely to vote for her, compared with only 35 percent of Republicans and 42 percent of Trump supporters saying they were more likely to vote for Trump. Public Policy Polling found that large shares of young people, Hispanics and African Americans all said the debate made them more likely to vote for Clinton.

In the first 30 minutes, it looked as if Trump might be able to clear even the low expectations that many in the media had set for him (and that his own campaign had encouraged). The debate’s opening question, on job creation, set him up nicely to focus on NAFTA and jobs going overseas, a subject on which Clinton is consistently on the defensive. Indeed, the only area where Trump made gains between the pre- and post-debate polls of the dial group was on trade.

Yet even the first half-hour had signs of Trump’s collapse to come. Clinton’s first rebuttal included a line needling Trump on the $14 million he borrowed from his father. It was a test of whether Trump had miraculously developed some discipline. He took the bait and characterized $14 million as “a very small loan.” It was clear that Clinton could bring up Trump’s baggage knowing that not only would he not change the subject, but he would also double down. Thus she could easily pivot between her own policy plans, knowing that he would get bogged down, and the parts of his record that would repel women, young people and other groups whose high turnout is her easiest path to victory.

The cringe-worthy moments piled up for Trump, such as saying that he rooted for the housing collapse because “that’s called business” and interrupting moderator Lester Holt’s question about “what do you say to . . . people of color . . .” with “I say nothing.” When Clinton suggested he might be hiding his tax returns because he doesn’t pay any federal income tax, Trump interjected, “That makes me smart,” seeming to imply that Clinton’s charge was correct. He also perpetuated the birther issue by repeating the debunked claim that Clinton’s campaign started it.  The tax returns and birther responses were easily some of Trump’s least popular answers with the dial group voters across the board. (Republican consultant Frank Luntz found similar results.)

Like in most elections, turnout is crucial at the presidential level. Turnout held Ohio for George W. Bush in 2004. It got Obama to beat the polls in a number of states in 2012. Trump has been struggling for months to catch up in the ground game; Clinton has to make that advantage count. If she can keep these voters energized until November, Election Day will be over quite early.