• A Parkinson's disease expert visited the White House several times over the past year, including a January meeting with President Biden's personal doctor, NBC News confirmed.
• Biden defended his 2024 candidacy in a last-minute television interview several hours before the reports of the Parkinson's doctor's visits.
• Nine House Democrats have so far publicly called on the president to bow out of the 2024 race following his debate fumble against Donald Trump, which intensified lingering concerns about the president's age.

A Parkinson's disease expert visited the White House several times over the past year, including a January meeting with President Joe Biden's personal doctor, NBC News confirmed on Monday.

Dr. Kevin Cannard, a neurologist who specializes in Parkinson's, visited the White House at least eight times over an eight-month period, as confirmed by public visitor logs stretching until March. Several news outlets previously reported the doctor's visits.

The logs did not specify why Cannard was at the White House, who he was there to see or whether Biden was present during his visits.

Biden's physical fitness has been a lingering public concern throughout his term. But those worries turned into a full-fledged panic when over 51 million viewers watched him stammer through the June debate against former President Donald Trump.

In response to the reports of Cannard's visits, White House spokesperson Andrew Bates said that Biden's medical exams have "found no sign of Parkinson's, and he is not being treated for it."

White House press secretary Karine Jean-Pierre didn't supply more information about the Parkinson's doctor's visits during Monday's press briefing.

"For security reasons, we cannot share names," Jean-Pierre said, though Cannard's name was included in the public logs.

"It doesn't matter how hard you push me. It doesn't matter how angry you get with me. I'm not going to confirm a name. It doesn't matter if it's even in the log. I am not going to do that from here. That is not something I am going to do," she said.

'Not going anywhere'

On Monday morning, Biden defended his place at the top of the Democratic ticket in a surprise television interview on MSNBC's "Morning Joe" and on a call with Democratic donors.

"I'm not going anywhere," Biden said in the televised phone interview. "I absolutely believe that I am the best candidate to beat Donald Trump in 2024."

Since Biden's disastrous debate performance on June 27, various Democratic donors have been sounding the alarm on whether he can beat Trump in November.

"I'm getting so frustrated by the elites in the party" calling for him to step down, the president fumed on MSNBC. "I don't care what the millionaires think."

Biden insisted to hosts Joe Scarborough and Mika Brzezinski that the concerns of his wealthy backers would not dictate his political future.

"I want their support, but that's not the reason I'm running," Biden said. "I'm not running about what they think and what they care about. And by the way, you don't see a whole hell of a lot of them flocking to Trump. You don't see a whole lot of CEOs flocking to Trump."

"I'm not going to explain any more about what I should or shouldn't do," the president added defiantly. "I am running. I am running."

Democratic worry on Capitol Hill

Biden's surprise MSNBC appearance came after a weekend where his political wounds appeared to deepen. Despite his campaign's efforts to stem the bleeding, more lawmakers, donors and strategists have gone public with their doubts.

On Monday, several Democratic senators came forward with statements presenting something of an ultimatum for the president, urging him to prove to the public that he has what it takes to defeat Trump and carry out a second term.

"President Biden has got to prove to the American people — including me — that he's up to the job for another four years. Meanwhile, I'll continue to do what I've always done: Stand up to President Biden when he's wrong and protect our Montana way of life," Sen. Jon Tester, D-Mont., said in a statement to NBC News.

Sen. Martin Heinrich, D-N.M., echoed that warning in his own statement, "President Biden needs to continue to demonstrate that his debate performance was just a bad night, and that he has a clear path to defeating Donald Trump."

Sen. Sherrod Brown, D-Ohio, in Youngstown on Monday said his constituents "have legitimate questions about whether the president should continue his campaign, and I'll keep listening to people."

The outpouring of comments came after the cancellation of a Monday meeting of Democratic senators reportedly organized by Sen. Mark Warner, D-Va., to discuss Biden's reelection concerns.

Warner on Monday issued a similar comment as his colleagues: "It is incumbent upon the President to more aggressively make his case to the American people."

The drop-out pressure has mounted even more on the other side of Capitol Hill.

During a meeting of senior House Democrats on Sunday, four more top Democrats told party leader Rep. Hakeem Jeffries of New York that Biden should exit the 2024 race, according to NBC News: Reps. Adam Smith, Wash., Jerry Nadler, N.Y., Mark Takano, Calif., and Joe Morelle, N.Y.

They joined five other House Democrats who had already publicly called on Biden to step down last week, including Rep. Angie Craig, D-Minn., who announced her position on Saturday.

On Monday, Biden sent a letter to congressional Democrats, doubling down on his commitment to stay in the 2024 race, as they all returned to Washington after the holiday recess.

"The question of how to move forward has been well-aired for over a week now. And it's time for it to end," Biden wrote in the letter. "Any weakening of resolve or lack of clarity about the task ahead only helps Trump and hurts us."

Damage control

Last week, Biden held several meetings and calls with Democratic lawmakers and allies, including former House Speaker Nancy Pelosi, Rep. Jim Clyburn, D-S.C., House Minority Leader Jeffries and Senate Majority Leader Chuck Schumer, D-N.Y.

Last Friday, Biden also sat for a 22-minute interview with ABC News' George Stephanopoulos, though it did not appear to resolve Democrats' anxieties.

In the coming week, Biden will be busy in meetings for the NATO summit in Washington where he has a dual-mandate: unify foreign allies around Ukraine support and quell Democratic Party concerns about his reelection bid.

On Thursday, Biden is scheduled to hold a news conference where all eyes will watch for if the president can redeem himself in an unscripted environment, receiving challenging questions. Biden is also expected to make more calls to lawmakers in the coming days to reassure them.

Some lawmakers see the week ahead as a decisive moment for the fate of Biden's campaign.

"The clock is ticking," Sen. Chris Murphy, D-Conn., a close ally of the president, said Sunday on CNN's "State of the Union." "This is going to be a really important and vital week for the country and for the President."

— CNBC's Josephine Rozzelle contributed to this report.

Correction: Several news outlets previously reported Cannard's visits. An earlier version misstated the breaking news source.