Biden was repeatedly pressed about his fitness to run. Here’s the latest.

In his first major interview since a dismal debate performance plunged his re-election bid into uncertainty, President Biden dismissed concerns about his health and doubts about his ability to win, saying only “the Lord Almighty” could convince him that he should step aside.

Throughout the 22-minute interview, recorded Friday afternoon and aired in prime time on ABC Friday night, George Stephanopoulos of ABC News repeatedly pressed Mr. Biden about his mental acuity and, more subtly, whether he was in denial about his ability to win the election.

Top allies of Mr. Biden’s and even, privately, the president himself have acknowledged that he must salvage his candidacy in the coming days, and this interview, along with an earlier campaign event in Wisconsin, came with high stakes. His stamina will be studied with concern. Just before the interview aired, Mr. Stephanopoulos said it was an unedited interview. “There are no cuts, no edits. We have not touched it.”

In the interview’s first minutes, Mr. Biden attributed his debate performance to exhaustion. “I was sick; I was feeling terrible,” he said, though he suggested that former President Donald J. Trump’s aggressive falsehoods had thrown him off balance. “I just had a bad night,” he said.

But questions about a bad night soon became an exchange, at times tense, about Mr. Biden’s age and concerns about his health, which Mr. Stephanopoulos said were widespread, and which Mr. Biden dismissed as the jitters of the press.

Toward the end of the interview, Mr. Stephanopoulos asked how Mr. Biden would feel in January if Mr. Trump were elected. Mr. Biden said that as long as he “gave it my all” and did a good job, “that’s what this is all about.” Then he pivoted. “Look, George,” he said. “Think of it this way. You’ve heard me say this before. I think the United States and the world is at an inflection point when the things that happen in the next several years are going to determine what the next six, seven decades are going to be like.”

Here’s what else to know:

• Biden says he has not seen a specialist for a neurological exam. Mr. Stephanopoulos asked Mr. Biden if he had “had a full neurological and cognitive evaluation,” and Mr. Biden said that he had one “every day” and that he had “a full physical.” Mr. Stephanopoulos followed up, asking if a specialist had done a neurological exam. “No,” Mr. Biden said. “No one said I had to. They said I’m good.” Asked if he would be willing to have an independent medical evaluation, including neurological and cognitive tests, and to release the results to the American people, Mr. Biden said: “Look. I have a cognitive test every single day. Every day I have that test. Everything I do. You know, not only am I campaigning, but I’m running the world.”

• A defiant campaign stop, and a vow to stay in the race. Mr. Biden spoke earlier Friday at a campaign event in Madison, Wis., where he cracked a few jokes about his age, described Mr. Trump as a threat to democracy and said he would not step aside — referring at one point to people trying to “push” him out. “I’m staying in this race,” Mr. Biden told the crowd, to cheers. “I’m not letting one 90-minute debate wipe out three and a half years of work,” he said. His next campaign event is on Sunday in Pennsylvania.

• More Democratic defections: Representatives Seth Moulton of Massachusetts and Mike Quigley of Illinois became the third and fourth House Democrats to publicly call for Mr. Biden to drop out of the race. Senator Mark Warner of Virginia is working to convene fellow Democratic senators to talk about President Biden’s future, according to five people with direct knowledge of the effort. And Representative Hakeem Jeffries, Democrat of New York and the minority leader, has scheduled a virtual meeting on Sunday with senior House Democrats. Separately, major donors are calling for Mr. Biden to step aside.

• A word with the media: Before boarding Air Force One in Wisconsin, President Biden approached the assembled reporters and said: “You’ve been wrong about everything so far, you were wrong about 2020, you were wrong about 2022. We were going to get wiped out — remember the red wave? You were wrong about 2023.” Mr. Biden also said that all of the Democratic governors he met with on Wednesday had urged him to stay in the race. Asked about a succession plan, he said: “By the way, we do have succession plans. But what do I need a succession plan for now?”

• Trump weighs in: Mr. Trump has largely laid low this week, preferring to let the spotlight shine uninterrupted on Mr. Biden’s crisis. But he posted a July 4 message on social media, deriding Mr. Biden, whom he accused of having “choked like a dog during the debate,” and Vice President Kamala Harris, who he suggested could replace Mr. Biden on the Democratic ticket. Mr. Trump’s next scheduled public campaign appearance is a rally in Florida on Tuesday.