Washington, July 8 : US President Joe Biden on Monday called upon Democratic lawmakers "to end" the heated debate over his candidacy for re-election, triggered by his disastrous debate, saying in a letter to them that "I am firmly committed to staying in this race".

Biden's letter seeks to quell a revolt brewing among Democratic lawmakers.

Four senior members of the House of Representatives - Jerry Nadler, Adam Smith, Mark Takano, and Joe Morelle - on Monday joined growing calls for him to step aside, taking the total to nine.

Senate Democrats are meeting later in the day to talk about Biden's candidacy later on Monday as called by Mark Warner.

The party turmoil entered the second week on Monday at the same time as NATO leaders are gathering here in Washington DC for their annual summit.

Allies will be keeping an eye on the embattled American President's domestic troubles as they discuss threats posed individually and collectively as a group by Russia, China, and Iran.

The Democratic party has been riven by a bitter debate triggered by his weak performance in the first presidential debate against former President Donald Trump, the presumptive Republican nominee, on June 27.

Some Democrats think he seemed not only incapable of defeating Trump in the election but also governing the country for the next four years, if he wins a second term. They have called for him to make way for someone younger and healthier.

Vice-President Kamala Harris is a leading contender.

But President Biden is not going anywhere.

"Despite all the speculation in the press and elsewhere, I am firmly committed to staying in this race, to running this race to the end, and to beating Donald Trump," he wrote in the letter.

"The question of how to move forward has been well-aired for over a week now. And it's time for it to end."

In a call to a morning talk show, Biden threw a challenge to those "party elites" who have been calling for his ouster to contest against him for the party nomination at the convention in Chicago.

"I'm getting so frustrated by the elites, I'm not talking about you guys, but about the elite in the party, who ' know so much more," Biden said, adding "challenge me at the convention".

Biden reminded lawmakers in the letter that he won the party nomination with 14 million votes, which was 87 per cent of the votes cast, and won nearly 3,000 party delegates (who will elect the nominee formally at the convention).

"This was a process open to anyone who wanted to run. Only three people chose to challenge me. One fared so badly that he left the primaries to run as an independent. Another attacked me for being too old and was soundly defeated. The voters of the Democratic Party have voted. They have chosen me to be the nominee of the party," he wrote.

"Do we now just say this process didn't matter? That the voters don't have a say? I decline to do that."

/IANS