WASHINGTON (AP) President Joe Biden has a fresh opportunity Thursday to try to prove to the American public that hes capable of serving another four years after his shocking debate flop threw the future of his presidency into doubt. But Biden is not known as a master of the big rhetorical moment and his recent cleanup efforts have proved inadequate.

Biden, 81, will close out the NATO summit in Washington an event meant to showcase his leadership on the world stage with a rare solo press conference . His stamina and effectiveness are under the microscope like never before and hes struggling to quell the Democratic Partys panic about his chances this November.

By many metrics, from job growth and major legislation to the expanded transatlantic alliance, Biden can point to successes during his tenure in office. But where he has sometimes failed spectacularly, in the case of the debate is at a defining part of the role that isnt in the official job description: delivering inspiring oratory that commands the attention and respect of the nation.

Biden has tried to step up his performance since the debate but his follow-up interview on ABC last week was disappointing. Nothing hes tried seems to be stopping the bleeding, with more lawmakers calling for him to bow out in the face of concerns that he could hand the White House back to Republican former President Donald Trump .

Americans tend to regard their leaders less for what they do than how they make them feel, and Bidens debate disaster has shaken his party to its core.

The debate was a reminder that you can have as many policies as you want, but what the public sees and hears might matter more, said Julian Zelizer, a Princeton presidential historian.

Rhetoric is intertwined with the modern presidency, from Franklin D. Roosevelts The only thing we have to fear is fear itself to Ronald Reagans Mr. Gorbachev, tear down this wall!

It can inspire in the wake of tragedy, like George W. Bushs bullhorn speech on the smoky rubble at ground zero after the Sept. 11, 2001, terrorist attacks and help a war- and recession-weary country recover its sense of self, like Barack Obama s Yes we can! Even Donald Trumps Make America Great Again cry echoed the temperament of the agitated nation.

People saw Trump as a reflection of a more turbulent, chaotic and angry country, Zelizer said. Voters may see Bidens frailty as a symbol of weakness or its own kind of instability.

Biden can give a good speech his State of the Union address earlier this year helped quiet doubters about his viability as a candidate. But his strength as a president and politician has been how his humanity in intimate settings resonated with voters, and the power of his personal narrative and down-to-earth roots.

Yet those moments, in private or before small crowds, even if amplified on social media as Bidens team hopes, are certain to reach fewer people than the tens of millions who watched his bout with Trump.

Despite a drumbeat of calls from some in his party to step aside, Biden has dug in, insisting hes the best Democrat to defeat Trump, whose candidacy hes called an existential threat to democracy.

His press conference will be closely watched for his ability to think on his feet, to demonstrate dynamism and to articulate both that he is still capable of doing the job and of winning it once more. To date, Biden has held the fewest news conferences, 37, since Ronald Reagan, who had held 25 at the same point in his presidency, according to research by Martha Kumar, a Towson University presidential scholar.