HEMPSTEAD, New York — Monday night’s presidential debate was an opportunity for Donald Trump to turn a new leaf in the race. The polls have tightened up after Labor Day, and his first one-on-one was a chance to come across as presidential and unflappable.

But even if the debate comes out as a wash, Trump made a few very significant errors: Each time Hillary Clinton baited him, Trump reacted, resulting in a series of Trumpian moments that are sure to give the Democrats fresh ammunition against him with just a few weeks to go before Election Day.

When Clinton said he’d wanted to take advantage of the real estate crisis, he said that was “called business, by the way.” He wouldn’t say if Russia is responsible for hacking Democratic email systems, instead raising the specter of a hypothetical 400-pound hacker. He said not paying federal income taxes “makes me smart.” He defended not paying contractors who have worked on his properties. He rekindled a feud with Rosie O’Donnell, whose appearance he has insulted, saying she “deserves” it. And he defended his long-running questioning of President Obama’s birthplace, arguing that he actually cleared up the controversy by getting Obama to release his birth certificate. (“I got him to give the birth certificate. So I'm satisfied with it. And I'll tell you why I'm satisfied with it.”)

Trump, in other words, handed reinforcements to the Clinton campaign in several different areas: foreign policy, Trump’s treatment of women, his business dealings, and to what extent he pays taxes.

Democrats in the post-debate spin room were openly celebrating the material Trump had handed them for future attack ads.

“I think the challenge there is it’s kind of an embarrassment of riches,” said former Obama campaign manager David Plouffe, adding, “Some of those moments — ‘Is it Russia or a 400-pound person on the bed?’ ‘Call Sean Hannity to find out if I opposed the Iraq War?’ — those were some bizarre moments.”

“It’s hard to tell at this point” exactly which Trump statements might make their way into future campaign ads, said Clinton communications director Jennifer Palmieri. But, she added, “there were important moments on both sides” that would be turned into fodder.

Clinton campaign pollster Joel Benenson, meanwhile, noted that Trump complained twice during Monday’s debate about the ads that have been aired against him.

"There's been no shortage of material created by Donald Trump, and in fact he can complain about all the ads that are being run, [but] every one of them is things he has said," Benenson said. "They are his words. If he doesn't like the ads that show his words in them, maybe he ought to think about changing some of the language he uses to describe people in America."

Jorge Silva, the campaign's Hispanic media director, foresees new ads springing from Trump's debate performance.

"Tax returns hurt him," Silva said. "But his comments on the birther issue killed him."