Biden is seeking to show during his whirlwind day with world leaders at NATO, and the evening press conference that he is up for another four years. Voters are watching, and elected officials are deciding whether to press for another choice.

But in 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.

Democrats are facing an intractable problem. Top donors, supporters and key lawmakers are doubtful of Biden’s abilities to carry on his reelection bid after his recent debate performance, but the hard-fighting 81-year-old president refuses to give up as he prepares to take on Republican Donald Trump in a rematch.

Biden 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. And it declared no other Democrat would do better against Trump.

“There is also no indication that anyone else would outperform the president vs. Trump,” said the memo from campaign chair Jen O’Malley Dillon and campaign manager Julie Chavez Rodriguez that was obtained by The Associated Press.

The memo sought to brush back “hypothetical polling of alternative nominees ” as unreliable and it 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 Vice President Kamala 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.

While Biden has expressed confidence in his chances, 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 well aware heading into the week there would be more calls for him to step down, and they were prepared for it.

The number of House Democrats asking that Biden step aside grew to a dozen on Thursday. In the Senate, only Peter Welch of Vermont has so far called for Biden to step out of the race.

Senate Majority Leader Chuck Schumer invited Biden’s team to meet with senators privately at the lunch hour to discuss concerns and the path forward, but some senators groused they would prefer to hear from the president himself.

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 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.

The fresh emphasis on the “blue wall” states by the campaign, which has heavily invested in other battlegrounds such as Arizona, Nevada, North Carolina and Georgia, acknowledges that the path to defeating Trump in November is narrowing, even as the team insists the Sun Belt states are “not out of reach.”

Though senior campaign aides write in the memo that Biden could clinch 270 electoral votes in a number of ways, it also says those three states are critical and that is why Biden has prioritized the areas in his recent travels. He went to Madison, Wisconsin; Philadelphia and Harrisburg, Pennsylvania over the weekend. He’s going to Detroit on Friday.

Polls conducted after the debate have largely agreed that Democrats nationwide have doubts about Biden’s ability to lead the ticket in November.

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