U.S. President Joe Biden will face the media Thursday for a highly important news conference that comes amid sustained pressure that he drop his bid for re-election.

The 81-year-old Biden has been participating in a NATO summit this week in Washington and the closing news conference — scheduled for 6:30 p.m. ET — could prove pivotal in assuring American voters that he's fit to serve another four years in the Oval Office.

Biden, the presumptive nominee for the Democrats, has been fighting to keep his re-election bid alive in the wake of a much-panned debate performance against Donald Trump, his 78-year-old presidential predecessor and Republican rival, two weeks ago. They are the oldest contenders to ever seek the Oval Office.

Thursday's news conference will be Biden's least scripted televised appearance since the debate — testing his mental acuity and ability to answer a flurry of questions from several reporters. He has not held a solo news conference in this manner since November, according to The Associated Press. 

Earlier on Thursday at the summit, Biden mistakenly referred to Ukrainian President Volodymr Zelenskyy as "President Putin" before correcting himself.

Zelenskyy is "going to beat President Putin," Biden said quickly. "I am so focused on beating Putin." 

More Democrats call for ballot exit

The pressure on Biden continued to build Thursday, as more House Democrats came forward urging him to exit to the ballot — now totalling at least 12 —  along with one Democrat senator.

Rep. Hillary Scholten of Michigan said on social media Thursday that Biden should "pass the torch."

Similarly, Rep. Brad Schneider of Illinois said in a statement that "the time has come ... for President Biden to heroically pass the torch to a new generation of leadership."

Rep. Greg Stanton of Arizona made a similar public appeal for Biden's departure, as did Rep. Ed Case of Hawaii.

Donors contributing to pressure

Biden has also seen key Democrat donors and supporters demanding the same, including Hollywood actor George Clooney who earlier this week wrote an op-ed calling for the president to step aside.

So far, Biden has resisted the calls to go, arguing he is best-placed to defeat Trump in the November election.

Some of the president's closest advisers — including Biden campaign chair Jen O'Malley Dillon — met with Democrat senators on Thursday to shore up support for his re-election bid. That did not seem to assuage all who attended.

"Some of my concerns are allayed, some others have been deepened," Sen. Richard Blumenthal of Connecticut said afterward.

Yet Biden still retains support among some prominent senators.

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