Donald Trump loves an audience.

But during his first debate with Hillary Clinton, he didn’t have one that could audibly respond to what he was saying — and the strain of trying to play to a mostly silent room quickly set him spinning.

"Donald was one of the people who rooted for the housing crisis," Clinton said early in the night, as the candidates dove into their plans for encouraging financial prosperity. "He said back in 2006, ‘Gee, I hope it does collapse, because then I can go in and buy some and make some money.’ Well, it did collapse."

Trump, leaning down to his microphone, didn’t wait for his turn to defend himself: "That's called business, by the way."

During the Republican primary debates, this self-promoting interruption likely would have earned some amused claps.

For the first presidential debate, during which the audience was forbidden from reacting, it died on the vine — and so, too, did many of the unscripted moments Trump tried throughout the night, the kinds of moments he has relied on throughout this campaign to keep the spotlight.

Trump loves a loud, applauding audience

Throughout an increasingly bizarre election, Trump’s affection for validation has been one of the few constants — and a predictable one at that.

After all, Trump’s blustering public persona was formed in the school of reality television. After investing his time, energy, and money into the bombastic parade that is the Miss Universe pageant, Trump made himself a star on The Apprentice, a show that claimed to celebrate sharp business acumen but mostly just celebrated the guy sitting across the boardroom table, chopping down potential employees, one by one.

And as we’ve seen frequently, Trump’s rise to become the Republican nominee for president of the United States is almost entirely thanks to his ability to keep the spotlight squarely on himself, no matter the subject, no matter who’s talking, no matter if he has anything of significance to say.

The Republican debates started with a dozen candidates dismissing the idea that Trump could be a contender — but they ended with a handful scrambling to throw insults back in Trump’s face as the crowd cheered him on with wild applause.

My colleague Libby Nelson performed an exhaustive study of Trump’s winning techniques throughout those Republican primary debates, and it should surprise no one that they’re all textbook reality show staples.

Trump speaks in catchy slogans. He deflects hard questions to tell stories that make him look good, no matter how relevant. He baits opponents into taking the low road, then takes the opportunity to slam them into the dirt. He makes winking references to behind-the-scenes preparations, to give people at home the feeling that he’s being realer than anyone else onscreen.

When all else fails, Trump talks until someone succeeds in cutting him off, exhausted, preferring to give up on getting an answer to the question they asked Trump, rather than keep listening to him hedge around the point.

Basically, every single trick Donald Trump used to win the Republican primary debates is a trick any Real Housewife worth her salt knows inside and out.

But on September 26, Trump had a significantly different task from any he’s had to tackle throughout his campaign: He had to play to a room that wasn’t allowed to applaud.

Trump slowly lost his way as the night went on without applause

To be sure, it’s not as if this rule entirely mattered, much to moderator Lester Holt’s frustration. A few cheers still slipped through the cracks, notably when Trump insisted that he’d release his tax returns once Clinton released her deleted emails (and the IRS was done auditing him). But for the most part, the audience was silent as requested, with only the occasional snickers cropping up throughout the debate.

Trump’s demeanor was immediately different once he had to face this new set of less-than-friendly circumstances. He’s used to commanding rooms that openly embrace his bluster, from the Republican primary debates to the halls he’s filled across the country — and whose audiences he’s curated by making sure protesters get kicked out.

But in the first presidential debate against Clinton, Trump had very little energy to work with from the audience. While he stuck to the same set of dependable lines in the debate’s opening section on the economy — most particularly lines about jobs leaving the country and the ongoing financial inequality in Michigan and Ohio — he quickly veered off during Clinton’s responses to interrupt her in sporadic jabs:

"Wrong."

"Lie."

"Wrong."

"Why not?"

In front of an audience that could respond, these asides might have gotten bigger responses. But standing in front of people who (mostly) honored the request to remain quiet, Trump’s go-to strategies didn’t work. He’d spit them out, and they’d hang there, waiting for a response, before fading into the ether.

Trump eventually tried to compensate for the lack of reaction with more aggressive interruptions, and, yes, a couple of those interruptions finally got traction toward the very end, as the audience lost patience with the rule and cheered. Many times, though, an attack from Clinton would send Trump into overcompensation, like when he responded to the accusation that he hadn’t paid an architect for one of his golf clubhouses with, "Maybe he didn’t do a good job."

For a showman like Trump, an audience that can’t applaud is a nightmare scenario. His campaign relies on giant statements, pointed jokes, and conspiratorial winking. None of these things work without some kind of response, and Trump had none of that as he fought off Clinton’s exhaustive fact-checking.

Even if the audience wasn’t entirely indifferent to him — and it wasn’t, judging by the eventual cheers at the end once people tired of the rule — that’s the impression silence gives. A veteran politician like Clinton, if nothing else, will know a silent audience isn’t always one that’s rejecting what you’re saying. Trump seemed more easily rattled.

If there’s one thing Trump’s never had to deal with on this campaign before, it’s indifference. Watching him try to push past the silence during this first presidential debate was like watching an improv comedian run through all his usual tricks and panic when none of them landed. Without the instant gratification of audible approval, he was awkward, stilted, and unsure of exactly where to interject.

He wasn’t, in other words, the Trump who won the Republican nomination — and if he can’t figure out how to exist outside the context of a wildly approving audience from now on, he might not be the one to win the presidential election, either.

Watch: How presidential debates are won and lost