It's almost hard to remember at the time of writing -- two hours later -- but dit nhau phu debefore the first presidential debate at Hofstra University Monday night, Hillary Clinton supporters were tying themselves into knots of anxiety.

The bar had been set incredibly low for Donald Trump. Pundits on every cable channel agreed: all he had to do was to get up on that stage and be, well, presidential. Stay calm, stay focused on his winningest issue -- the economy -- and don't allow yourself to get baited by Clinton.

SEE ALSO: I tried to ignore Trump for a whole month. Here's what I learned.

Well, as the world now knows, Trump couldn't even stay calm long enough to stop arguing with (and talking over) moderator Lester Holt. Avoiding Clinton's bait? Fuggeddaboutit. Trump might as well have ended the debate with a mouth full of fish hooks.

Every network's instant poll of viewers showed Clinton winning the debate by a significant margin. Panels of undecided voters stampeded her way like she was a Black Friday sale (18 to 2 in CNN's panel). Even Trump's strongest surrogate, Rudy Giuliani, conceded that it was not the boss' best debate.

And those famous dial tests, where voters are given the option of registering their approval or disapproval of what a candidate is saying in real time, went through the floor every time Trump prevaricated, talked over Clinton or rambled -- even when it was a longtime Republican pollster like Frank Luntz controlling the dials.

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By any measure, for Trump, the debate can be described using one of his favorite words: disaster. This was a golden opportunity for him. The polls had tightened to a dead heat, and looked worse than ever for Clinton in the all-important swing states. Post-pneumonia, questions about her health seemed, for the average voter, to be increasingly legitimate.

All Trump had to do was turn in a reassuring performance for the folks at home -- something he's done a thousand times on The Apprentice. Then sit back, smile and let his spinmeisters do the rest.

For the first 10 to 20 minutes, Trump seemed fully capable of executing this strategy. Twitter may have lost its mind about his sniffing, but those of us who've been around the block a few times -- who remember George W. Bush sniffing like a coke-addled freight train in his first debate with Al Gore in 2000 -- know that this is no impediment to winning the presidency.

It wasn't the sniffing that lost the debate. It was Trump's inability to prepare, to focus, to restrain his ego, to stay calm when faced with evidence that he has lied -- heck, his inability to finish sentences. Sentences.

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Trump spoke nearly twice as much as Clinton, by the numbers. He tried to dominate the debate by sheer force of words. In the end, though, the more he spoke, the worse it got for him.

Clinton, by contrast, had a dream debate. She looked calm and comfortable throughout, moderated her voice, smiled all the smiles that male pundits had suggested she smile over the course of the last year -- but doing so in her own time, on her own terms.

Her little shoulder shimmy after a red-faced Trump went nuclear attacking her temperament said it all. The Long Island audience -- home turf for Trump, pretty much -- couldn't help itself, laughing at the notion that this woman, patiently waiting her turn, somehow had a worse temperament than the candidate who was yelling at her.

SEE ALSO: No amount of dressing can save Donald Trump's debate word salad

You couldn't help but feel for a candidate who gets talked over (roughly 50 interruptions from Trump) and shouted at like that, and still keeps coming. This is Hillary's strategy: Roll with the punches, then calmly give as good as she gets. Many have criticized it in the past. Nobody is doing so tonight.

She managed to get off a few pre-prepared slogans, though I doubt we'll be talking about "Trumped up trickle-down economics" in a few weeks' time. (I had to do a Google search just to word it correctly.)

More importantly, she kept the focus on areas that needled Trump: His disgraceful support for the "birther" movement, and his even more disgraceful lack of an apology. His laughable claim, still to be found on Twitter, that climate change is a Chinese conspiracy. His repeated and blatant misogyny.

These are not good looks for Trump, and yet he could not allow himself to move on. Determined to gaslight America en masse, he denied every statement he'd ever made that showed him in a bad light. "Wrong, wrong, wrong," he shouted at one point, talking over Clinton and jabbing at the podium.

Every parent could recognize in that moment the temperament of a child who is losing an argument.

We have to wait to see how much this moves the polls and the swing states, of course. Trump has proven himself to be made of teflon before. We know that millions of Americans are willing to let themselves be gaslighted. Maybe the estimated 100 million who tuned in only watched the first 15 minutes.

The memory of this debate may fade by Nov. 8. Trump "the calm reassuring presidential figure" may show up next time around. But in the immediate aftermath, it's hard to see how things could have gone worse for the GOP candidate. He looked like a petulant, red-faced cartoon, exactly what Democrats and #NeverTrump supporters have said he was all along.

Hillary Clinton won the debate. But we would be remiss to not give a giant assist to Donald J Trump, his own worst enemy.