The president sent a letter to House Democrats, saying it's time to move on from the debate.
One senior Illinois representative said he's all in for Biden.
Biden remains adamantly committed to his campaign for reelection despite concerns within his own party that he may not be up for another four years.
On Monday, the president sent a letter to Democratic members of Congress, saying he firmly believes he's the party's best chance in November.
"We have one job. And that is to beat Donald Trump. Any weakening of resolve or lack of clarity about the task ahead only helps Trump and hurts us," Biden wrote.
Congressman Danny Davis said he needs no convincing.
"Joe Biden is the candidate. He's my candidate, and he's America's champion. And we need to keep him there," said Rep. Davis, D-Chicago.
The president was on MSNBC Monday morning, saying voters have spoken.
"All the data shows that the average Democrat out there who voted, the 14 million of them have voted for me, still want me to be the nominee," Biden said.
But, with polling suggesting Biden now trails Donald Trump in many battleground states, the lone member of the Illinois congressional delegation calling for the president to step aside defended that statement again Monday morning.
"I think we have to be honest with ourselves; the situation is not getting better. Frankly, it's getting worse," said Rep. Mike Quigley, D-Chicago. "What I would stress to the president: This isn't just about you. It's not about loyalty; it's about being pragmatic. We have to be honest with ourself. It's not just the White House at stake."
On a call with major donors Monday, the president tripled down on staying in the race, vowing to go on the attack in the next debate.
On Tuesday, House and Senate Democrats will meet separately in Washington to discuss the situation.
Congressman Davis, who is older than Biden, said age should not be part of the discussion.
"I have not seen anything that I could describe as cognitive decline (in Biden)," Davis said.
Republicans hope Biden doubts will help local GOP candidates
Republicans hope Biden doubts will help local GOP candidates
Meanwhile, Republicans at at a Palatine dinner Monday night feel confident ahead of a consequential convention and hope the current Democratic Party turmoil will translate to GOP wins locally.
"It's a really exciting time. It's a scary time for our future as an American, but we have a real opportunity to embrace positive change," said House Minority Leader State Rep. Tony McCombie.
The Northwest Suburban GOP Lincoln Day Dinner came one week before the start of the Republican National Convention in Milwaukee.
"Donald J. Trump, you heard it first here, is going to win a 40-state reelection landslide!" said former Trump senior economic advisor Stephen Moore.
Republicans there said doubts about Biden will benefit GOP candidates locally.
"We look at a lot of our state rep races, a lot of our senate races and our congressional races that are moderate districts, and we are so encouraged to have more wins in those areas because the Democratic Party right now is self-destructing," said Palatine Township Republican Committeeman Aaron Del Mar.
The Democratic National Convention is in just 42 days. Capitol Hill Democrats are planning to meet in Tuesday morning to discuss next steps.
"I think he needs to continue to get out and be in front of the American people, to speak without the teleprompter in front of people. Show us the Joe Biden that we knew four years ago," said Democratic U.S. Rep. Brad Schneider, who represents the north and northwest suburbs.
For the president, his next major test begins Tuesday, when the three-day NATO Summit gets underway in Washington, and world leaders will be making their own assessment of the president.