Key moments from Biden's critical press conference

President Joe Biden, under the microscope as Democrats debate his political future, tried to make the case that he is best suited to take on Donald Trump this November and finish what he's started in a second term.

In a nearly hourlong solo press conference, Biden faced a room full of reporters for the first time since his poor debate performance two weeks ago sent his party into a panic about his mental fitness and ability to carry out his campaign.

Almost all questions posed to the president focused on those issues, with Biden on defense on everything from his cognitive health to whether he believes his vice president could take on the role.

The president remained adamant that he believes he is the most qualified person to go up against Trump.

"I beat him once, and I will beat him again," Biden said.

Here are several key takeaways Biden's press conference.

The gaffes continue

Answering the first question of the night, Biden made a glaring error when he confused Vice President Kamala Harris with Trump.

"Look, I wouldn't have picked Vice President Trump to be vice president, if I didn't think that she's not qualified to be president, so let's start there, number one," Biden said after being asked if he had concerns about Harris' ability to beat Trump if she ever found herself at the top of the ticket.

He also addressed the mistake he made earlier Thursday during the NATO summit when he introduced Ukrainian President Volodymyr Zelenskyy as "President Putin."

A reporter asked him about the gaffe and whether, when paired with some reports that world leaders privately expressed concern about his age, America's standing on the world stage was being damaged.

"Do you see any damage by me leading this conference?" Biden responded. "Have you seen a more successful conference? I was talking about Putin and I said -- at the very end -- I said, 'Putin. I'm sorry, Zelenskyy.'"

Biden: 'I've gotta finish the job'

Biden said he realizes the importance of allaying fears and plans to do so by letting the American people see him out on the trail making the case for why he should get a second term.

He spent considerable time railing against gun violence, attacks on reproductive rights and the broader dangers that he said would be posed by a Trump presidency.

"Do you think our democracy is under siege based on this [Supreme] Court? Do you think democracy is under siege based on Project 2025?" Biden said. "Do you think he means what he says when he says he is going to do away with the civil service and eliminate the Department Education?"

"I mean, we've never been here before," Biden said. "And that's the other reason why I didn't, as you say, 'hand-off to another generation.' I've got to finish this job. I've got to finish this job. Because there's so much at stake."

Biden says he needs to 'pace' himself

Biden said he needs to "pace myself a little more" when pressed on how he is up to the 24/7 nature of the presidency, but argued that he is kept busy while his 2024 rival is not.

"Since I made that stupid mistake in the campaign -- in the debate, I mean, my schedule has been full-bore," Biden said.

"Where has Trump been? Riding on his golf cart and filling out his scorecard?" Biden said. "He has done virtually nothing. I've had roughly 20 major events, some with thousands of people showing up."

Biden said he has always had an inclination to "keep going" and that his staff is always adding events.

Biden cedes others could beat Trump but argues he's most qualified

Biden's long argued that he alone can defeat Trump after having done so in 2020.

"I think I am the best qualified -- I know -- I believe I'm the best qualified to govern," Biden said. "And I think I am the best qualified to win."

"But there are other people who could beat Trump, too," he acknowledged before quickly adding that it would be "hard" for Democrats to start from the beginning.

A reporter then followed up by asking Biden if he would reconsider his decision to stay in the race if his team showed him polling data that Vice President Harris would fare better against Trump.

"No, unless they came back and said there is no way you could win. Me," Biden said. "No one's saying that. No poll says that."

A new ABC News/Washington Post/Ipsos poll found Biden continues to run evenly with Trump: Americans were divided 46-47% between Biden and Trump if the election were held today. Were Harris to replace Biden as the Democratic nominee, the poll found Harris leading Trump 49-46% among all adults and 49-47% among registered voters.

On taking a cognitive test, Biden says 'no one's going to be satisfied'

Asked if he was going to take a cognitive test before the election, Biden said that he would take one if his doctor advised him he needed one.

Biden said he has taken three "significant" neurological exams during his presidency, most recently in February.

"They say I am in good shape," he said. He then reiterated that he is tested "every single day" on his neurological capacity by simply doing his job as commander in chief.

"And I'll ask you another question, no matter what I did, no one's going to be satisfied," Biden said. "Did you have seven [doctors]? Did you have two? Who'd you have? Did you do this? How many times did you -- so, I am not opposed if my doctors told me I should have another neurological exam, I'll do it. But that's where I am."

Biden takes tough stance on Russia, China

The press conference came off the heels of a weeklong gathering of NATO leaders in Washington, and Biden took the opportunity to emphasize his leadership on the world stage during several exchanges.

On Russia and China, Biden said he is "ready to deal with them now and three years from now."

Biden said no world leader has spent more time with Chinese President Xi Jinping than him, and that they will continue to negotiate. When it comes to Russian President Vladimir Putin, Biden said he saw "no good reason" to speak with him now but would be prepared to do so.

"There isn't any world leader I'm not prepared to deal with," Biden said.

ABC News' Meredith Deliso and Ivan Pereira contributed to this report.