President Joe Biden reacted to the debate in a post on X early Wednesday morning.

"America got to see tonight the leader I've been proud to work alongside for three and a half years. Wasn't even close," he said.

Biden was in New York City during the debate and will be attending the 9/11 memorial services at Ground Zero later in the day.

A majority of debate watchers think Harris won the debate against Trump, according to a poll taken by CNN and SSRS after the debate.

On who won the debate, 63% of debate watchers said Harris and 37% said Trump.

The poll has a margin of error of +/- 5.3% points.

CNN said that before the debate, respondents were split 50%-50% on who would win.

In June, their instant poll found that among debate watchers, 33% thought Biden won and 67% thought Trump won.

-ABC News' Oren Oppenheim

Harris put Trump on the defensive early on, claiming viewers were "going to hear from the same old, tired playbook, a bunch of lies, grievances and name-calling." She later took digs at his rallies and was the first to bring up his multiple indictments.

Meanwhile, Trump tried to tie Harris to President Joe Biden as often as he could. "She is Biden," he said as he criticized their economic record.

Harris' gender was not broached during the debate, though her race was. Trump doubled down on false claims about her racial identity, though he said he "couldn't care less."

Read more about the debate highlights here.

During the Harris-Trump face-off, both candidates tried to score points by slinging barbs at each other.

Here are some of their sharp jabs:

Trump: “Wait a minute, I'm talking now, if you don't mind, please. Does that sound familiar?”

Harris: “Donald Trump was fired by 81 million people.”

Harris: “He talks about fictional characters like Hannibal Lecter.”

Read more zingers here.

Trump campaign spokesperson Danielle Alvarez said Tuesday morning on ABC News Live that Trump "does not do traditional debate prep" and reiterated that he has been campaigning and engaging in policy discussions instead.

"I would say that the president does not do traditional debate prep. He's on the campaign trail constantly. We see him in key battleground states every week, joined by tens of thousands of patriots," she said. "We know that he does tough interviews, both nationally, locally."

"That's truly how he prepares for these debates, having those conversations every day. He's ready to step back into the White House," she continued. "We also know that he prefers to have those policy discussions, and he's been doing that with elected members in Congress like Matt Gaetz, with former Congress member Tulsi Gabbard and others -- very similar to what he did to prepare for that first debate against Joe Biden. He has prepared in a similar way again, just by getting out there and talking every day to voters and talking to media."

-ABC News' Soorin Kim, Lalee Ibssa and Kelsey Walsh