WASHINGTON (AP) — President Joe Biden used his closely watched news conference Thursday to deliver a forceful defense of his foreign and domestic policies and batted away questions about his ability to serve another four years, declaring: "I'm not in this for my legacy. I'm in this to complete the job."

Early on, he made one notable flub when he bobbled a reference to Vice President Kamala Harris. But for an hour, he largely held his own under intense questioning, eschewing any suggestion that he was in decline, no longer capable of leading the nation and too old to serve another term.

It was unclear whether the performance was enough to change the dynamic that has set in: A growing number of Democratic lawmakers, donors and celebrities are calling on him to step aside — not to mention the majority of voters expressing doubts that he is up to the job — and Biden is digging in, insisting he's staying in the race and will win come November. And the longer the infighting continues, the less the Democrats are presenting a united front against Republican Donald Trump.

"If I slow down and I can't get the job done, that's a sign that I shouldn't be doing it," Biden said. "But there's no indication of that yet — none."

Yet even as he wrapped his news conference, the 81-year-old leader was confronting calls to step aside. In a statement released shortly after he walked offstage, Connecticut Rep. Jim Himes, the top Democrat on the House Intelligence Committee, said Biden should end his candidacy, considering his "remarkable legacy in American history." Fifteen other House Democrats have called on him to make way for a new candidate.

Vintage Biden during the news conference

Biden said he was willing to take another neurological assessment before the election, but only if his doctors recommended it. His last exam was in January and the results of it were released in February.

In his first exchange with reporters, Biden was asked about losing support among many of his fellow Democrats and unionists, and was asked about Vice President Kamala Harris. Biden was at first defiant, saying the "UAW endorsed me, but go ahead," meaning the United Auto Workers. But then he mixed up Harris and Trump, saying, "I wouldn't have picked Vice President Trump to be vice president if she wasn't qualified."

Trump weighed in live on Biden's news conference with a post on his social media network of a video clip of the president saying "Vice President Trump."

Trump added sarcastically, "Great job, Joe!"

Most of news conference was vintage Biden: He gave long answers on foreign policy and told well-worn anecdotes. He used teleprompters for his opening remarks on NATO, which ran about eight minutes. Then the teleprompters lowered and he took a wide range of questions from 10 journalists about his mental acuity, foreign and domestic policy and — mostly — the future of his campaign.

"I believe I'm the best qualified to govern and I think I'm the best qualified to win," Biden said, adding that he will stay in the race until his staff says there's no way he can win.

"No one's saying that," he said. "No poll says that."

Biden has explained away his June 27 debate performance as a bad night following a grueling month of international travel. Since then, he's been out in public more, talking with voters and answering reporters' questions. He even looks considerably less pale than he did two weeks ago.

"I'm determined on running but I think it's important that I allay fears — let them see me out there," Biden said.

But his campaign on Thursday acknowledged he is behind, and a growing number of the president's aides in the White House and the campaign privately harbor doubts that he can turn things around.

But they're taking their cues from Biden, expressing that he is in 100% unless and until he isn't, and there appears to be no organized internal effort to persuade the president to step aside. His allies were aware heading into the week that there would be more calls for him to step down, and they were prepared for it. But they felt like he met the moment Thursday, and demonstrated to lawmakers and the public he could do the job even though he's not known as a polished speaker.

The news conference extended into prime-time television coverage, and the major TV networks broke into programming for it, meaning millions of Americans were likely to have seen it.

Campaign acknowledges president is behind but sees path to win

Earlier, Biden's campaign laid out what it sees as its path to keeping the White House in a new memo, saying that winning the "blue wall" states of Wisconsin, Pennsylvania and Michigan is the "clearest pathway" to victory.

The memo sought to brush back "hypothetical polling of alternative nominees" as unreliable and said such surveys "do not take into account the negative media environment that any Democratic nominee will encounter."

Meanwhile, the campaign has been quietly surveying voters on Harris to determine how she's viewed among the electorate, according to two people with knowledge of the campaign who spoke to The Associated Press on condition of anonymity to talk about internal matters.

The people said the polling was not necessarily to show that she could be the nominee in Biden's place, but rather to better understand how she's viewed. The research came after Trump stepped up his attacks against Harris following the debate, according to another person familiar with the effort. The survey was first reported by The New York Times.

The other major flub of the day

His other major flub of the day came before the press conference, while announcing a compact that would bring together NATO countries to support Ukraine. Biden referred to the nation's leader Volodymyr Zelenskyy as "President Putin" to audible gasps in the room. He quickly returned to the microphone: "President Putin — he's going to beat President Putin ... President Zelenskyy," Biden said.

Then he said, "I'm so focused on beating Putin," in an effort to explain the gaffe.

"I'm better," Zelenskyy replied. "You're a hell of a lot better," Biden said back.

Biden campaign meets with senators

In an effort to bring together anxious lawmakers with Biden's team, Senate Majority Leader Chuck Schumer organized a meeting to discuss concerns and the path forward, but some senators groused they would prefer to hear from the president himself. In the Senate, only Peter Welch of Vermont has so far called for Biden to step out of the race.

The 90-minute conversation with the president's team, which one person said included no new data, polling or game plan on how Biden would beat Trump, did not appear to change senators' minds. The person was granted anonymity to discuss the closed door session.

The meeting was frank, angry at times and also somewhat painful, since many in the room know and love Biden, said one senator who requested anonymity to discuss the private briefing. Senators confronted the advisers over Biden's performance at the debate and the effect on Senate races this year.

One Democrat, Sen. Chris Murphy of Connecticut, said afterward: "My belief is that the president can win, but he's got to be able to go out and answer voters' concerns. He's got to be able to talk to voters directly over the next few day."

At the same time, influential senators are standing strongly with Biden, leaving the party at an impasse.

Sen. Bernie Sanders, the Vermont independent, told the AP he thinks Biden "is going to win this election. I think he has a chance to win it big."

Sanders said he has been publicly critical of the campaign, and said Biden needs to talk more about the future and his plans for the country. "As we come closer to Election Day, the choices are very clear," he said.

__ Associated Press writers Michael Balsamo, Mary Clare Jalonick, Kevin Freking, Farnoush Amiri and Linley Sanders contributed to this report.