President Biden, who in the past has batted away questions about his advanced age by telling skeptics to “watch me,” will have one of the most consequential audiences of his political career as he steps to the lectern in Washington and faces a horde of journalists on Thursday. Members of Congress, Democratic donors, party strategists, voters, foreign leaders and officials within his own White House are planning to tune in for what is expected to be a real-time test of Biden’s ability to think on his feet and deliver under pressure.

The pivotal event comes as Biden is trying to save his candidacy and convince Democrats that his faltering debate performance last month was simply a “bad night” and not indicative of a broader decline in his cognitive abilities. The outsize importance of the news conference also underscores how Biden’s attempts over the past two weeks to downplay his debate stumbles and move forward with his presidential campaign have so far failed to convince many in his party.

Even as the president has defiantly declared that he will stay in the race and shored up his support this week by winning over key constituencies, the number of top Democrats who have remained silent or voiced only tepid support indicates that a poor showing at the news conference could unleash a fresh wave of defections. Anxious Democrats fear Biden’s weak showing in polls and halting public appearances could pave the way for Donald Trump’s return to the White House, a prospect some have described as an existential threat to the country’s democracy.

Sen. Richard Blumenthal (D-Conn.) said Wednesday that he remained “deeply concerned” about Biden’s prospects against Trump, joining the chorus of Democrats who have argued that Biden needs to do more in the days ahead to reassure voters and lawmakers.

“I think he needs to continue effectively and aggressively making his case to the American people and earning their support, as well as a number of my colleagues,” he said.

Biden’s aides have suggested that the president’s activity over the past two weeks — which has included multiple rallies, a handful of interviews, some well-received speeches, impromptu conversations with supporters and a hosting role at the NATO summit in Washington — have helped him stem the calls for him to drop out of the race. Campaign officials pointed to the president’s defiant letter Monday asserting that he would remain in the race and highlighted the statements of support he has received from some Democratic officials in recent days.

Still, several party leaders remain skeptical, and some have warned that Biden’s inability to quickly bounce back from the debate with public displays of vigor has been particularly concerning. Democratic lawmakers have said for days that they wanted to see Biden in more unscripted settings, speaking without notes or a teleprompter, to show that the debate in which he often struggled to complete his sentences was just a one-off.

That the news conference is coming a full two weeks after the debate has struck some in the party as a telling sign, and several Democratic aides and lawmakers have predicted that the president will perform poorly before a press corps primed to ask challenging questions about his age and acuity.

Several congressional aides and some lawmakers, speaking on the condition of anonymity to discuss private deliberations, said they see the news conference as the first real test of the 81-year-old’s cognitive abilities since the June 27 debate, noting that he will not have a script and will have to navigate a wide-ranging set of questions. The event caps NATO’s 75th anniversary summit, which Biden hosted this week, though questions about his political standing and health are likely to dominate.

Biden will face reporters at a time when many in his party are demoralized over his weak standing in the presidential race, in the wake of several polls showing him trailing Trump in key swing states. While Trump, 78, is only slightly younger than Biden, voters have expressed far more concern about Biden’s ability to serve as president for four more years. In a New York Times-Siena College poll released after the debate, 74 percent of voters viewed Biden as too old to serve effectively as president; 42 percent said the same about Trump.

On Tuesday, Sen. Michael Bennet (D-Colo.) said on CNN that he feared Biden was on track to lose to Trump in a “landslide” and that the White House needed to do more to “demonstrate that they have a plan to win this election.”

On Wednesday, Biden faced a new round of skepticism, with more lawmakers either calling for him to step aside or saying they wanted him to show more political vitality before they could fully support him. Sen. Peter Welch (D-Vt.) became the first senator to publicly call on Biden to step aside, in an opinion piece for The Washington Post. Speaking on MSNBC’s “Morning Joe,” former House speaker Nancy Pelosi (D-Calif.) repeatedly urged Biden to make a decision about whether to stay in the presidential race, despite the president’s insistence that he has already made up his mind to remain at the top of the Democratic ticket.

Also on Wednesday, George Clooney, the Hollywood actor and a top fundraiser for Biden’s reelection, called for the president to be replaced as the Democratic nominee. In a New York Times op-ed, Clooney, who hosted Biden for a fundraiser last month, suggested that the president was losing the battle with time.

“It’s devastating to say it, but the Joe Biden I was with three weeks ago at the fundraiser was not the Joe ‘big F-ing deal’ Biden of 2010,” Clooney wrote. “He wasn’t even the Joe Biden of 2020. He was the same man we all witnessed at the debate.”

The flurry of doubt surrounding the president raises the stakes for his news conference, according to several Democratic officials, who indicated they will be watching closely for any stumbles or signs of weakness. For their part, Biden’s aides are hoping a solid showing Thursday will help him finally put the drama over the debate in the rearview mirror.

Supporters and detractors alike have noted that timing could be in Biden’s favor. If he makes it through the news conference without sparking a fresh round of intraparty panic, focus will begin to shift toward Trump and the Republicans, who are holding their nominating convention next week. Trump is expected to announce his running mate in coming days, and Congress will be out of session next week.

Biden has not always performed well at major solo news conferences, which have been rarities during his presidency.

In January 2022, Biden stood before reporters for nearly two hours, fielding inquiries on a wide range of issues and occasionally getting testy with journalists who asked pointed questions.

After the event, first lady Jill Biden berated the president’s aides for allowing the event to go on so long, according to the book “American Woman: The Transformation of the Modern First Lady, from Hillary Clinton to Jill Biden.”

Since then, the president has held significantly fewer substantive engagements with the media compared with his predecessors.

Biden has participated in 36 news conferences during his presidency, the fewest of any president during the same period since Ronald Reagan, according to data compiled by Martha Joynt Kumar, professor emerita of political science at Towson University and the director of the White House Transition Project.

Biden has largely favored so-called two-by-two news conferences, in which he addresses the media while standing next to a foreign leader, with questions limited to two journalists from each country’s delegation. He often keeps his answers brief, rarely engaging in the kind of lengthy, professorial responses embraced by former president Barack Obama or the long-winded riffs by Trump.

In recent press appearances, Biden has occasionally read his answers from notecards rather than speaking extemporaneously. His voice at times has been low and gravelly. He has sometimes mixed up names or stopped himself midsentence rather than completing his thought, with Republicans seizing on each flub.

White House aides, who often determine which journalists are called on, have occasionally tried to fish out the substance of reporters’ questions ahead of the events, a practice that predates Biden’s presidency but has gained additional scrutiny due to the focus on the president’s mental acuity.

Two radio hosts said Saturday that they were supplied questions from Biden aides before separate interviews with him last week, a practice the campaign initially defended but later said it would refrain from going forward.

Republicans responded by suggesting that Biden was not mentally fit to answer unscripted questions. Officials from the Republican National Committee — who have become adept at taking clips of Biden’s stumbles at public appearances and circulating them — have often lambasted the president during news conferences and suggested, without evidence, that the events are scripted.

In addition to the content of his answers and his delivery, the president’s demeanor will also be in focus as party officials scrutinize whether he appears vigorous enough to carry Democrats’ message against Trump in coming months.

Biden has sometimes bristled over reporters’ attempts to ask multiple questions or lashed out at journalists who query him about issues that he considers off-topic.

The conference will cap a NATO summit during which the president announced that new F-16 fighter jets would be going to Ukraine; praised member countries for increasing their defense spending; and awarded the Presidential Medal of Freedom to NATO Secretary General Jens Stoltenberg.

While several journalists are likely to query Biden on Thursday about the 2024 race and the issues that have come to dominate it — his age, health and political standing — world leaders will also be watching the news conference to see whether the president shows proficiency and deftness on a range of global issues.

For his part, Biden has suggested that he will use his future public appearances to challenge Trump more directly, and he told donors Monday that he would take a different approach to a future debate with the presumptive Republican nominee.

“Attack, attack, attack, attack,” he said.

Jacqueline Alemany, Leigh Ann Caldwell, Marianna Sotomayor, Mariana Alfaro and Liz Goodwin contributed to this report.