Donald Trump exploded on the debate scene in the Republican primaries and his opponents were at first completely flummoxed. He dominated them effortlessly and endlessly. His sheer size, his focused anger, his ability to steal the camera away from everyone else even when he wasn’t speaking thanks to his facial reactions, and his big open gestures – all added up to a presence the more traditional politicians didn’t know how to handle.

To be sure, they developed some coping strategies, but on body language alone, Trump won the primaries by several lengths. The only moment when someone else gave him as good as she got occurred when Carly Fiorina called him out on his rude comments about her earlier in Rolling Stone. She said, “I think women all over the country heard very clearly what Mr. Trump said,” and for once Trump was quiet –momentarily.

Last night the country got to see Trump go head to head with Hillary Clinton, and the question was would he dominate as effortlessly as he did in the primaries or would we witness something more like a Fiorina moment? Would Trump’s anger and bluster work as well with only two people on the stage, or would Clinton’s reserve play better? Who, in short, would win the body language debate?

I always pay close attention to the walk-on body language of the debaters, because before the candidates even open their mouths they’re showing their stuff. In this case, Clinton hit the stage first, showing confidence. She had a big smile on her face, a strong, confident walk, interacted easily with the crowd and the moderator, and shook Trump’s hand at mid-stage.

Trump, in contrast, was a little slower coming on, his walk was a bit more tentative, his smile was fake, what we body language geeks call a non-Duchenne smile, and his head was slumped forward in the head posture – signaling less enthusiasm about being there than Mrs. Clinton.

So before the debate even started formally, Clinton had the edge.

But then the first fifteen minutes of the debate, in terms of body language, were all Trump’s. The topic was trade, one of his strong suits, and he interrupted confidently, called out Clinton, and generally dominated most of the exchanges. What worked for him in the primaries appeared to be working again. Clinton allowed herself to be interrupted and talked over, and didn’t appear to be as strong. Her preparation and reserve seemed to be hampering rather than empowering her, though from the start her mastery of the facts was far stronger than Trump’s.

But who needs facts in this election cycle? Indeed, they were getting in Clinton’s way, threatening to make her appear bloodless and wonky rather than caring. Where were the stories? I settled in for what looked to be another Trump walk away.

Then, as the evening wore on, the body language balance surprisingly started to shift. Once the debate moved to less comfortable ground for Mr. Trump, his body language fell apart. His interruptions became more frequent, and shrill, and made less sense. He seemed like a child with no effective answer, even reduced to saying “not true, not true,” at one point, like the arguments I used to have with my sister when we were eight: I did not – yes, you did – no I didn’t – yes, you did – and so on. Only Clinton played the grownup in these exchanges, responding coolly while Trump looked uncomfortable and sounded unconvincing.

And Clinton landed zinger after zinger, for which Trump had no adequate response, from his taxes to his racism to his careless talk about nuclear war to his denigration of women, to his “birther” lies, and finally to his rude remarks about the Hispanic “housekeeper”: “Donald, she has a name. Her name is Alicia Machado. And she has become a U. S. citizen, and you can bet she’s going to vote this November.”

But what really gave the game away was Trump’s increasingly unbalanced body language. His head tipped to one side, his shoulders tipped the other way, and his grimaces started to look peevish, even loutish. He clutched the podium with one hand, while finger-pointing with the other. His voice rose, both in volume and tone, sounding uncertain and anxious. What had been dominance became pettishness. His responses became more erratic and monosyllabic and, when he did go on, wandering. He was sweating under his makeup and swigging the water freely. Clinton, by contrast, stayed calm, didn’t drink once during the entire debate, and never lost her poise.

Who won the body language debate? Clinton, after a slow start. Mr. Trump’s powerful, ad-libbed style, that worked so well in the primaries, let him down in the end last night.