WASHINGTON, July 9, 2024 (BSS/AFP) - President Joe Biden insisted again Monday he would not quit the US election race, as the White House denied he had Parkinson's disease following a disastrous debate performance.

The 81-year-old dared Democratic critics to either challenge him at next month's party convention in Chicago or back him against Donald Trump in November's vote.

The president lashed out in both a letter to Congress and a rare call to a television program, at the start of a critical week that includes a NATO summit in Washington where he will face fresh scrutiny.

"I am firmly committed to staying in the race," Biden wrote in the letter.

"It is time to come together, move forward as a unified party and defeat Donald Trump," he said. "It's time for it to end."

The embattled president followed up by phoning into MSNBC's "Morning Joe" television program to say he was "getting so frustrated by the elites" in the party.

"Any of these guys that don't think I should run -- run against me. Announce for president, challenge me at the convention," he added.

But even as he doubled down, the pressure mounted on the oldest president in US history.

Congressman Adam Smith, the senior Democrat on the US House Armed Services Committee, said Biden should step aside.

"I think it's become clear he's not the best person to carry the Democratic message," he told CNN.

- Parkinson's denial -

Biden's blitz was a clear attempt to lay to rest the spiralling concerns over his health following the June 27 debate against Republican Trump, whom he trails in the polls.

During the debate Biden repeatedly lost his train of thought, stared blankly and spoke at times incoherently and with a raspy voice. Biden has blamed jetlag and a cold.

The White House has also felt the pressure, with tense exchanges at a press briefing on Monday.

Press Secretary Karine Jean-Pierre called for "respect" while journalists challenged her refusal to confirm reports that a Parkinson's specialist visited the White House eight times.

The visits by Kevin Cannard, a neurologist from the Walter Reed National Military Medical Center where Biden receives his medicals, were recorded in publicly available visitor logs.

"Has the President been treated for Parkinson's? No. Is he being treated for Parkinson's? No, he's not. Is he taking medication for Parkinson's? No," Jean-Pierre said.

The White House also denied reports that NATO allies attending this week's 75th anniversary summit in Washington had shown concerns about Biden.

"We're not picking up any signs of that from our allies at all," National Security Council spokesman John Kirby told reporters.

But NATO leaders have been seeking reassurance in any case amid polls forecasting a November victory for Trump.

The former president has long criticized the defense alliance, voiced admiration for Russian strongman Vladimir Putin, and insisted he could bring about a quick end to the war in Ukraine.

- 'All in' -

The NATO summit begins on Tuesday, the same day that Democrats, returning to Capitol Hill from a brief recess, hold a caucus meeting where Biden's fate will be discussed.

In recent days, five Democratic lawmakers have publicly called for him to drop out of the race -- with Smith becoming the sixth.
On Sunday US media said four senior congressmen -- including Smith -- said on a call with party lawmakers that it was time for Biden to bow out.

The Democrat lags behind Trump in most polls even though his rival was recently convicted of a felony in a porn star hush money case.

But efforts to force out Biden will not be easy.

First Lady Jill Biden has fiercely defended her husband and did so again on Monday at the start of a trip to Georgia, Florida and North Carolina.

"For all the talk out there about this race, Joe has made it clear that he's all in," she at a veterans' event in Wilmington, North Carolina.

Numerous allies have also weighed in.

The head of the Congressional Black Caucus, Steven Horsford, said on Monday that Biden had been "selected by millions of voters across this country."

Democratic Senator Chris Coons of Biden's home state Delaware told reporters it would be a "huge mistake" to ditch the president.