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.

It's a hallmark of the American electoral process: the presidential debate.

The first nationally televised debate in history featured John Kennedy and Richard Nixon. The visuals did not play in Nixon's favor, as he was seen sweating and looking pale after previously being hospitalized for an infection, while Kennedy looked young and gave a more vigorous performance.

More than 20 years later, Ronald Reagan, the oldest sitting president at the time, shut down some questions about his age during his debate with Democrat Walter Mondale.

In 1992's trilateral debate, President George H.W. Bush was criticized for looking down at his watch. In 2000, Al Gore was mocked for his audible sighs during his debate with George W. Bush.

In the 2020 Democratic primary, one highlight was Harris' challenge to Joe Biden on the issue of segregation and busing, which prompted her viral quote, "That little girl was me."

Most recently, the debate between President Biden and Trump changed the course of the 2024 campaign after Biden's poor performance exacerbated Democratic and voter concerns about his age and fitness to serve another four years. He announced he was exiting the race 24 days later.