Defiant Biden throws down gauntlet to Democrats

President Joe Biden insisted again Monday he would not quit the U.S. 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.

Trump has been uncharacteristically quiet since the debate but he did speak out Monday on Fox News to say he thinks Biden will resist the pressure and stay in the race.

"He's got an ego and he doesn't want to quit," Trump said in an interview with Sean Hannity.

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

Congressman Adam Smith, the senior Democrat on the U.S. House Armed Services Committee, became the sixth Democratic lawmaker to publicly say Biden should step aside.

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

Other senior Democrats voiced support for Biden,...