Republican presidential nominee Donald Trump vowed to "hit harder" after a disappointing first debate against Democratic rival Hillary Clinton and doubled down on his criticism of a former Miss Universe winner's weight.
Mrs Clinton, meanwhile, sought to keep her momentum going as the candidate generally regarded as having won the debate, questioning her opponent's temperament and capitalising on his comments that evading federal taxes made him "smart".
Both candidates returned to the campaign trail after Monday's debate, which was watched by 84 million people - a record audience for a United States presidential debate.
Mr Trump was to hit the road in Illinois, Iowa and Wisconsin, all on Wednesday. Mrs Clinton deployed Senator and former rival Bernie Sanders, her daughter Chelsea and First Lady Michelle Obama from North Carolina to New Hampshire, mainly targeting the kind of college voters that helped propel US President Barack Obama to the White House.
In an attempt to put a positive spin on what many saw as a poor debate performance, Mr Trump suggested on Tuesday that he had shown respect and restraint during the debate.
"I was going to hit her with her husband's women. And I decided I shouldn't do it because her daughter was in the room," he told Fox News.
When asked how she would deal with personal attacks about her husband's infidelity, Mrs Clinton took the high road and told reporters on her campaign plane: "He can run his campaign however he chooses... I will continue to talk about what I want to do for the American people."
Mr Trump also defended his criticism of former Miss Universe winner Alicia Machado, whom Mrs Clinton used as an example of Mr Trump's disrespect for women.
Mr Trump accused the moderator of asking him "very unfair questions" and said he had a "very bad" microphone.
Former New York Mayor and Trump adviser Rudy Giuliani told reporters he would skip the next debate if he were Mr Trump, unless he was promised a more impartial moderator. But top aides say Mr Trump does plan to attend the second debate, though more rigorous preparation is being planned, reported the New York Times.
Brushing off his excuses, Mrs Clinton told reporters: "Anyone who complains about the microphone is not having a good night."
Speaking later at a rally in North Carolina, Mrs Clinton rehashed the previous night's exchange with Mr Trump on releasing his tax returns.
"He actually bragged about gaming the system to get out of paying his fair share of taxes. In fact, I think there's a strong probability he hasn't paid federal taxes a lot of years," she said. "He probably hasn't paid a penny to support our troops or our vets or our schools or our healthcare system," she added.
Mr Trump attended a fund-raiser in Miami, Florida, and a town hall-style meeting with Latinos, where he told his supporters: "We did very well."
"It was an interesting evening certainly, and big league," he said, according to the Miami Herald.
A CNN/ORC poll of voters who watched the debate found that Mrs Clinton beat Mr Trump 62 per cent to 27 per cent.
Some of his supporters also expressed their disappointment in online chat groups. The Daily Beast reported that on 4chan, an alt-right forum that Mr Trump and his campaign surrogates used to find memes and images for use on Twitter, someone posted: "Trump actually sucked tonight. "
But a number of online polls - which are non-scientific - including those conducted by CNBC and Time, showed that Mr Trump had actually won the debate. Fans interviewed by US media outlets at his rallies also continued to support him.
In a radio interview, President Barack admitted he was biased in his support for his former secretary of state, but noted that Mrs Clinton was "well prepared" and has the "right temperament" for the job of president.
By contrast, Mr Obama said Mr Trump "doesn't have the preparation, the temperament or the core values of inclusion... that would take our country forward".