Game changer for Hillary Clinton? No, no quite. But what happened at the debate was this: She showed that this is a marathon, and a candidate has to be able to go the whole distance. She showed she can. He didn’t.

Donald Trump tried to be serious. And in some ways, he was. He didn’t say anything totally crazy. He told some lies, about opposing the Iraq War , for example. And about his birtherism . But in many ways, he tried to be a serious discussant of policy—and even kind of pulled it off at times.

However: A serious discussion of policy is a debate held on Clinton’s turf. Trump’s big mistake, perhaps, was to depart from the bluster. He wins, as he showed in the Republican primary debates, when he writes the rules. He came into this debate trying to play according to the normal rules. And under normal rules, he loses, because he can’t follow them.

One of the key things that Clinton had to think about coming into this debate was how she looked when she wasn’t talking. That, she handled well. She didn’t roll her eyes. She didn’t too much laughing. She didn’t do too much of that Al Gore condescending, eye-rolling, liberal-elite sneering that made the candidate listening look worse than the one who was talking in the 2000 debates. She clearly trained for that, and it paid off.

For the first hour or so, it was kind of a rope-a-dope performance by Clinton. She let him punch himself out. For the first 20 minutes or so, some of the punches landed. On trade, and on other issues. But then Trump started to over-punch, especially in the way he interrupted Clinton repeatedly.

Then, in the closing 30 or 40 minutes, she went into him hard, on his failure to release his tax returns in particular. Trump tried to hit her hard, on ISIS, but the punches didn’t quite land.

I could go into issues. But really, the particular issues don’t matter here so much. These things are about affect. As the wise heads say, you can watch these things with the sound down. And I would imagine that if you did watch this one with the sound down, Trump looked petulant and, well, low-energy.

Clinton wasn’t awesome. But she was prepared, she was solid, she did a good job. Trump, interestingly, overthought it. He kept going back and forth between grimacing and being rude to her on the one hand and on the other hand trying to say to America, “Hey, I’m thoughtful!” But that’s impossible, because no one, not even—or perhaps least of all—the people who love him think he’s thoughtful.

I always watch these things and try to think of how undecided voters saw it. It’s always a really hard thing to imagine. My sense is that this will move the needle only marginally in Clinton’s direction. She just looked more at ease. He looked effortful. And what was all that sniffing ?

But here’s what Clinton’s camp needs to keep this in mind: Trump does a lot of things that are conventionally “wrong” that don’t hurt him. They don’t hurt him because his voters are convinced that he’s their man, no matter what he feels he has to say to placate the politically correct crowd. They won’t desert him.

Her challenge is to reach the voters who aren’t Trump diehards but who drifted to him over the last couple of weeks as these polls have tightened for whatever set of reasons. She probably did that Monday night, but mainly because Trump was bad. She should be celebrating, but she should also bear in mind that there are two more of these, and Trump will adjust. This was a win for her, but I sense that questioning voters need to see her do this one more time, and she’ll face a different Trump next time.

But she showed Trump that this is a marathon. His over-rehearsed remark toward the end that she didn’t have the stamina came off as lame. She out-staminaed him Monday night in a big way.