PHILADELPHIA: US President Joe Biden was back out on the campaign trail Sunday, desperate to salvage his reelection bid as senior Democrats meet to discuss growing calls that he quit the White House race. The 81-year-old Democrat took the stage at a predominantly black church in Philadelphia, part of a two-stop swing in the battleground state of Pennsylvania, before he hosts the NATO leaders’ summit in Washington later this week.

He is campaigning under an increasingly unforgiving spotlight, as pressure mounts for him to drop out after his disastrous debate against Donald Trump last month ignited panic over his age and fitness to serve another four years. Biden has remained defiant, unequivocally declaring he is fit to serve, the only one who can defeat Trump, and staying in the race.

So far, five Democratic lawmakers have called on Biden to drop out, with the drumbeat of dissent slowly rising.

On Sunday, two high-profile congressional Democrats stopped short of calling for Biden to step aside, but warned that he still needed to win over voters worried about his age. "There’s only one reason” the race between Trump and Biden "is close, and that’s the president’s age,” Representative Adam Schiff told NBC’s "Meet the Press.” As some speculate about Biden handing off the campaign to Vice President Kamala Harris, Schiff added: "I think she very well could win overwhelmingly.”

Democratic Senator Chris Murphy meanwhile said "the president needs to do more,” including unscripted events like town hall gatherings, to reassure voters he has the mental acuity and physical fitness for a second term. "This week is going to be absolutely critical,” Murphy told CNN’s Sunday talk show "State of the Union”.

Those comments came as House Minority Leader Hakeem Jeffries has scheduled a virtual meeting of senior Democratic representatives for Sunday to discuss the best way forward, and Democratic Senator Mark Warner is reportedly working to convene a similar forum in the upper chamber. First Lady Jill Biden, who — according to some US media reports — is urging her husband to stay in the race, is scheduled to campaign for him Monday in Georgia, Florida and North Carolina.

But after Sunday’s stops in Philadelphia and Harrisburg, the president will have to step away from the trail for the NATO summit beginning Tuesday. Here, too, he will find himself having to reassure allies at a time when many European countries fear a Trump victory in November. The 78-year-old Republican has long criticized the transatlantic defense alliance as an unfair burden on the United States, voiced admiration for Russian strongman Vladimir Putin, and insisted he could bring about a quick end to the fighting in Ukraine, where Moscow’s invasion is in its third year.

For now, Democratic heavyweights are largely keeping a lid on any simmering discontent with their leader — at least in public. But with election day just four months away, any move to replace Biden as the nominee would need to be made sooner rather than later, and the party will be scrutinized for any signs of more open rebellion.

Meanwhile, for Biden and his team, the strategy seems to be to ride it out. The campaign has unveiled an intense battle plan for July, including an avalanche of TV spots and trips to all the key states. That includes a visit to the US Southwest during the Republican convention July 15-18, at which Trump is set to be anointed the party’s official presidential nominee.

In what had been billed as a make-or-break Friday interview with ABC News, Biden flatly dismissed his falling poll numbers and concerns over his fitness triggered by his dismal June 27 performance against Trump. But some of his answers were tentative or meandering, even as he deflected questions about his mental acuity and dismissed the notion his party would consider replacing him. "If the Lord Almighty came down and said, ‘Joe, get out of the race,’ I’d get out of the race,” he said. "But the Lord Almighty is not coming down.”

The Biden campaign had another small fire to put out Saturday after it emerged that the White House had provided the questions for interviews the president gave to two black radio stations on Friday. When pressed in the ABC interview on why he doesn’t take an independent neurological exam, Biden argued that the role of US president meant being subjected to constant mental assessment. "I have a cognitive test every single day,” he said. "Not only am I campaigning, I’m running the world.”

Democratic strategist David Axelrod suggested in a CNN op-ed that Biden is engaged in "Denial. Delusion. Defiance.” "The stakes are as great as Biden describes. And if he believes it, as I think he does, he will eventually do what duty and love of country requires, and step aside,” Axelrod wrote in the piece published Saturday. "If he does not, it will be Biden’s age, and not Trump’s moral and ethical void, that will dominate the rest of this most important campaign and sully the president’s historic legacy.”

Trump, meanwhile, sarcastically suggested Biden should "ignore his many critics and move forward, with alacrity and strength”. "He should be sharp, precise and energetic, just like he was in The Debate,” the Republican challenger said in a social media post Saturday. Two letters are circulating among House Democrats calling for Biden to step aside, House Democratic sources have said. Many of those lawmakers had been waiting to see the ABC News interview before moving forward. – Agencies