• Nancy Pelosi refused to explicitly endorse President Joe Biden as the party's presidential nominee.
• Pelosi also suggested that Biden has not made up his mind about whether to stay in the race, despite Biden's repeated insistence that he will not drop out and that his decision is final.
• Biden is busy with the NATO Summit this week, where he faces an added pressure to show Democrats that he is fit enough to beat Trump in November.

Former Democratic House Speaker Nancy Pelosi on Wednesday refused to explicitly endorse President Joe Biden as the party's presidential nominee, and encouraged her colleagues in Congress to pause from making public statements either for or against Biden.

"Let's just hold off. Whatever you're thinking, either tell somebody privately, but you don't have to put that out on the table until we see how we go this week," Pelosi said on MSNBC's "Morning Joe."

Several hours after Pelosi's interview, House Rep. Pat Ryan, D-N.Y., became the latest House Democrat to publicly call on Biden to step aside and let a new nominee come forward.

Pelosi's comments were notable because Biden has repeatedly insisted that he will not drop out of the race against former President Donald Trump, and said that his decision is final.

Pelosi's carefully worded comments suggested she believes Biden is still deciding whether or not to remain atop the ticket.

"It's up to the president to decide if he is going to run," Pelosi said. "We're all encouraging him to make that decision because time is running short."

Pelosi has long been one of Biden's closest allies in Congress, so her refusal to support Biden as the nominee — as scores of Democrats already have — sent ripples across the Capitol on Wednesday.

Pelosi spokesperson Ian Krager rejected the notion that her comments indicated slipping support for the president: "Speaker Pelosi fully supports whatever President Biden decides to do. We must turn our attention to why this race is so important: Donald Trump would be a disaster for our country and our democracy."

Pelosi's remarks came two weeks into Biden's wall-to-wall push to prove to Democrats and voters that his halting, feeble debate performance on June 27 was just "an episode," as Pelosi put it last week, and not evidence of "a condition." So far, Biden's public outings have done little to quell Democrats' concerns about his health.

"I'm not going anywhere," Biden said this week in an interview, also on "Morning Joe." "I absolutely believe that I am the best candidate to beat Donald Trump in 2024."

As a result, this week, Biden's NATO summit events in Washington come with the added pressure of proving to Democrats that he is fit enough to beat Trump in November and serve a second, four-year term.

On Monday, Biden will sit for an interview with NBC Nightly News anchor Lester Holt. This is the same day Biden is scheduled to give remarks in Austin, Texas commemorating the anniversary of the Civil Rights Act. The interview will come more than a week after his televised ABC News sit-down last Friday, which failed to quiet Democratic alarm.

The pressure for Biden to deliver redeeming public performances this week comes as voices calling on him to drop out get louder.

On Tuesday, Sen. Michael Bennet, D-Colo., became the first Democratic senator to publicly announce that he does not believe the president can beat Trump, though he did not go so far as to officially call for him to exit the race.

On Thursday, senior Biden advisors Mike Donilon and Steve Ricchetti, along with Biden Campaign Chair Jen O'Malley Dillon will speak to Senate Democrats during a special caucus lunch, a Senate Democratic leadership source told NBC News.

On the other side of Capitol Hill, the pressure has been more openly expressed. Also Tuesday, House Rep. Mikie Sherrill, D-N.J., added to the growing list of House Democrats to officially urge the president to leave the race.

House Minority Leader Hakeem Jeffries, D-N.Y., has told concerned caucus members that he will voice their worries to Biden, four sources confirmed to NBC News. Politico first reported that news.

"We're having conversations with ourselves. It's a family discussion, that's important," Jeffries told NBC News in response to a question about his plan to convey lawmakers' concerns to Biden. "We have the right and the responsibility on behalf of the people that we represent to have these conversations with ourselves about the path forward and the best interest of the American people, and that's all we're doing right now."

Over the past several days, Jeffries has organized several private meetings to hear out House Democrats' worries about Biden's vulnerabilities and the potential threat to down-ballot races.

In those types of closed-door meetings and other private calls, Democratic lawmakers, donors and strategists have expressed concerns about Biden's fitness to mount a grueling campaign and then, should he win in November, to spend another four years in the Oval Office.

In response to Pelosi's comments, the Biden campaign pointed to a letter the president sent to congressional Democrats on Monday, reiterating his dedication to stay in the race and calling on lawmakers to rally behind him. The campaign also laid out a list of Democratic lawmakers who have made public statements expressing support for Biden.

— CNBC's Josephine Rozzelle contributed to this report.