Donald Trump came into Monday night's debate with undeniable momentum. And the general consensus among pundits is that he squandered it with an ill-prepared, abrasive, petulant performance.
It's a good idea to take such assessments with a big grain of salt. We have been here too many times before – Mr. Trump delivering a performance that by any traditional standard would be considered disastrous and disqualifying, then either suffering no apparent damage or recovering quickly. And with an electorate this polarized, few people are likely to have their minds changed because of broad perceptions about which candidate performed better.
Was this time different? It depends whether Mr. Trump did himself serious damage with memorable moments or images – ones that will live on in clips through the rest of the campaign and beyond it in lore – that either confirm the worst fears of voters accessible to him or cause those currently in his camp to lose faith.
In a debate's immediate aftermath, it's really hard to tell what will stick. But here are a few guesses of how, if at all, Mr. Trump may have done himself real damage (and with whom).
Acting like a robber baron (white working class)
To this point in the campaign, Mr. Trump – who was born into wealth and has spent much of his life bending rules to his advantage and steamrolling over the less fortunate – has managed to position himself as a blue-collar champion. Even if his personal story has not been remotely relatable, his plain-spokenness and visceral anger have been. But in at least a couple of instances on Monday, he practically rubbed his privilege in the face of supporters in economically hard-hit parts of battleground states.
The moment getting the most attention was one in which Hillary Clinton goaded him into seemingly acknowledging he had avoided paying any income tax some years – years in which people with a lot less money than him paid their fair share. "That makes me smart," he interjected.
Perhaps even worse, when Ms. Clinton accused him of having rooted for the financial crisis that cost millions of Americans their homes, savings or jobs, he couldn't help himself from another interjection: "That's called business, by the way."
Mr. Trump appears to think embracing his most cutthroat behaviour as a businessman helps his cause because it proves he would be similarly cutthroat on behalf of his country. He hasn't exactly been disproved so far this campaign. But if "cares about people like me" is as important a perception about candidates as pollsters tend to think, the Republican nominee really pushed his luck.
Reinforcing perceptions of sexism (college-educated women)
As a general rule, a male politician in the 21st century should not say "She deserved it." But there was Mr. Trump, in the debate's final minutes, using precisely those words to justify once calling Rosie O'Donnell "a fat pig." And that came right after he looked flustered while Ms. Clinton accused him of once referring to a Hispanic beauty-pageant contestant as "Miss Piggy" and "Miss Housekeeping."
It was as much a matter of tone as any one line that may have hurt Mr. Trump with female voters, though. After beginning calmly, he spent much of the rest of the debate trying to talk over Ms. Clinton – interrupting her approximately 50 times during a 90-minute debate.
It wasn't quite a sequel to Rick Lazio, Ms. Clinton's opponent during her 2000 Senate bid, who torpedoed his campaign during a debate by leaving his podium to confront her at hers in what was subsequently cast as sexist bullying. But a candidate who desperately needs to parlay his recent momentum into headway with college-educated women – with whom he has still been polling abysmally – may have instead made it harder for many who have previously voted Republican to get past his personality.
Getting bogged down in birtherism (African-Americans)
Mr. Trump was unlikely to have a major breakthrough with African-American voters regardless of what he did Monday. But he's lately been trying to lower that demographic's antipathy toward him, if only to make it more difficult for Ms. Clinton to achieve the same turnout levels Barack Obama did – a potential difference-maker in key states.
It's safe to say that the way to build goodwill with those voters is not to remind them that he spent most of the first black president's time in office trying to discredit him with the lie that Mr. Obama was born in Kenya.
Mr. Trump had no choice in the matter coming up during the debate – it was moderator Lester Holt's decision. But if he had any contrition, he could have acknowledged he was wrong; if he had any discipline, he could have pivoted quickly to another topic. Instead, as at other points of the debate when he was put on the defensive, he went down a rabbit hole, making his latest attempt (including the invocation of political insiders most people have never heard of ) to advance a replacement lie that Ms. Clinton was more responsible for birtherism than he was.
Very, very few African-Americans (or others) who take this issue as evidence of Mr. Trump's bigotry are likely to be moved positively by his absurd ramblings on it. And even fewer can be expected to buy what might have been his most clippable line of this segment: that he did a "great service" to Mr. Obama by raising the profile of a racist conspiracy theory against him.
Acting unhinged (Republicans who recently came home)
There's a common theory that the best way to judge a debate's impact is to watch with the sound off, because body language matters most. Anyone who did that might have noticed a bunch of instances in which Mr. Trump visibly lost his cool, while Ms. Clinton laughed him off. But there was at least one segment, likely to get replayed a fair amount, in which Mr. Trump's tendency to project his own liabilities onto others made for some unfortunate audio as well.
At the end of a bit in which steam practically came out of his ears as he angrily and disjointedly denied he had supported the Iraq War (which he is on record as doing), Mr. Trump could not stop at saying he had better judgment than his opponent. "I also have a much better temperament than her, you know?" he said to a burst of laughter from the audience, before rambling on a while and accusing a bemused Ms. Clinton of recently acting "out of control." (The studio audience appeared to be made up heavily of partisans who as the evening went on increasingly ignored instructions to stay quiet, but this still sounded pretty bad.)
By this point of the campaign, Mr. Trump's volatile manner is already baked into most voters' perceptions. But it is probably not a coincidence that his surge in the polls through this month – which has largely involved people who usually vote Republican deciding they could live with their nominee – came as he kept his demeanour more in check than previously. Now he may have encouraged more talk, on cable networks and around kitchen tables, about his stability.
Failing to land a glove on his opponent (wavering Democrats)
For all the moments that may have hurt him, Mr. Trump may also suffer for his failure to sow further doubt among likely Democratic voters who have been uninspired by their candidate.
After attaching the "Crooked Hillary" label to her in recent months, he didn't so much as mention the Clinton Foundation, whose ties to the State Department over which she presided make for one of his usual attack lines. He did briefly take aim at her use of private e-mail servers while Secretary of State, but lacked the discipline to really press her on that scandal, instead circling back to a confusing defence of not making public his tax returns public.
While she repeatedly got under his skin, not once during the hour-and-a-half did he cause her to say something she would regret.
It may be that all moments from this debate will be distant memories by the time the next one is over. But just about all the ones with potential staying power, relevant to voters who stand to decide the election, threaten to put wind that was in Mr. Trump's sails until Monday behind Ms. Clinton's instead.
Editor's Note: An earlier version of this column incorrectly stated that Donald Trump was defending the fact that he has not filed his tax returns. In fact, he was defending not making his tax returns public. This version has been corrected.