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.

The Trump campaign during a pre-debate call said Trump is in "good spirits" and will be departing shortly for Philadelphia.

"President Trump is in good spirits. He is currently in Mar-a-Lago. My understanding is that he will be departing shortly to head over to Philadelphia," said Trump campaign senior adviser Danielle Alvarez when asked about his mood going into the debate.

She suggested that the former president is "ready" to talk about inflation, housing affordability and the border among other issues on the debate stage. Alvarez also suggested that Trump might attack Harris for flip-flopping on some key issues such as fracking, police funding and electric vehicles.

"The president is certainly full of surprises. I know that we can expect him to be, you know, with his, his charming self. We know that he is incredible when it comes to weaving in and out of topics -- he's incredible on those policy issues. So that's ... certainly something that may happen," she said.

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