Things started cheerily enough, with the president’s appearance on Kimmel’s semi-regular series, “Celebrities Read Mean Tweets.” It was Obama’s second time participating in that—dramatically reading the criticisms people had tweeted at his expense—and an extremely funny one. Some of the tweets the president read:

— Barack Obama is the Sharknado of presidents. Loud, stupid and over-hyped. #sharknado4

— Obama couldn’t negotiate getting a whopper without pickles.

— I just found out my daughter shares a birthday with Obama. PUKE!

— My mom bought a new conditioner and it sucks. It isn’t even conditioning my hair. I blame Obama.

Obama concluded his reading, however, with a specially selected mean tweet: “President Obama will go down as perhaps the worst president in the history of the United States!”

Obama paused. The tweet was from @realdonaldtrump.

He paused again, getting the timing perfectly.

“Well, @realdonaldtrump, at least I will go down as a president,” Obama said. Then he dropped the mic smartphone.

During Kimmel’s interview segment, though, things stayed on the topic of Trump but took a much more serious turn. The two engaged in typical small talk—about the mozzarella sticks backstage that Obama snacked on, about the Cubs’ participation in the World Series, about Bill Murray’s recent meeting at the White House—but quickly moved on to politics. Obama and Kimmel discussed Hillary Clinton: In response to Kimmel’s question about why so many people seem to distrust her, the president explained that “a lot of this just has to do with the fact that she has been in the trenches, in the arena, for 30 years.” They talked about Obama’s post-presidency life, and the family’s plan to stay in Washington. “I’m like the old guy in the bar where you went to high school,” Obama joked—“just kind of hanging around.”

But then: Trump. Trumpety-Trump Trump. “When you watch Trump in the debate,” Kimmel asked, “do you ever laugh?”

“Most of the time,” Obama replied.

They talked about the Access Hollywood video. “I think that’s one of those things where, if your best friend who worked in the office somewhere had that video, it’d be a problem for him,” Obama said. “And he’s not running for president.”

Things built, then, to another Trump question. “Do you ever wish you were running against Donald Trump?” Kimmel asked. “Do you ever wish you were in there?”

“You know, I think Hillary’s doing just fine,” the president responded.

After a moment, though, he added:

We joke about Donald Trump, but I do think that part of the reason you’ve seen Michelle so passionate in this election, part of the reason that we get involved as much as we have, is not just because we think Hillary is going to be a great president, but it’s also because there is something qualitatively different about the way Trump has operated in the political sphere.

And this is where the President Obama of 2016 had his moment of reckoning with the President Obama of 2011. The appropriate response to Trump, he suggested, is no longer to laugh him off. It’s no longer to do what a late-night show used to be all about: to mock the candidates in an equal-opportunity way. We are beyond that now. Late-night comedy is also, in some sense, beyond that. “Look, I ran against John McCain,” the president said. “I ran against Mitt Romney. Obviously, I thought that I could do a better job. But they’re both honorable men, and if they had won, then I wouldn’t worry about the general course of this country.”