US President Joe Biden was attending a black church and rallying union members on Sunday in the critical swing state of Pennsylvania, trying to project enough strength for his re-election campaign to quell a growing clamour from within in his own party for him to bow out of the race.

Mr Biden urged supporters to stay unified behind him at a rousing church service where the pastor referenced biblical teachings in declaring “never count Joseph out”, and blamed jealousy for intensifying pressure from some Democrats to abandon his re-election bid.

Speaking from a stage at Mount Airy Church of God in Christ in northwest Philadelphia, the 81-year-old Mr Biden laughed off concerns about his age, joking “I know I look 40” but “I’ve been doing this a long time”.

“I, honest to God, have never been more optimistic about America’s future if we stick together,” Mr Biden said. He did not use a teleprompter, which has become more common since his disastrous debate performance last month but spoke from a prepared speech.

His remarks followed Pastor Louis Felton likening Mr Biden to Joseph and the biblical story of his “coat of many colours”. Joseph was sold into slavery in Egypt by his jealous brothers, only to eventually obtain a high place in the kingdom of the pharaoh and have his brothers beg him for assistance without initially recognising him.

“Never count Joseph out,” Mr Felton implored. Then, referring to Democrats who have called on Mr Biden to step aside, he said: “That’s what’s going on, Mr President. People are jealous of you. Jealous of your stick-to-itiveness, jealous of your favour. Jealous of God’s hand upon your life.”

Mr Biden’s appearance came after he joined a Saturday call with campaign surrogates, and reiterated that he has no plans to step aside, while urging unity among top Democrats.

But he also listened to concerns and feedback, according to two people who spoke on condition of anonymity to discuss private conversations.

The president pledged on the call to campaign harder going forward and to hit the road more frequently, taking his message to voters more directly. He was attending a church service at Mount Airy Church of God in Christ in northwest Philadelphia, then going to the state capital of Harrisburg to speak at an organising event with union members and local Democrats.

Election 2024 Biden
US President Joe Biden, standing in back row at second from right, attends a church service at Mount Airy Church of God in Christ in Philadelphia on Sunday (Manuel Balce Ceneta/AP)

Later, Mr Biden visited a campaign office in Philadelphia, telling those assembled “we need you to continue for the next 121 days” before the election.

Also on hand was Senator John Fetterman, a Pennsylvania Democrat who won a tough 2022 race while recovering from a stroke and offered a forceful endorsement of Mr Biden, saying: “That’s our president, that’s your president, that’s my president.

“There is only one guy that has ever beaten Trump and he is going to do it twice and put him down for good,” Mr Fetterman said.

On Sunday evening, Mr Biden returns to Washington, where leaders from Nato countries will gather for a three-day summit beginning on Tuesday to mark the military alliance’s 75th anniversary.

The focus could shift more to Russia’s war in Ukraine than questions about Mr Biden’s re-election campaign, but the 81-year-old’s political situation remains precarious.

Five Democratic lawmakers have called on him to abandon his re-election bid ahead of November, and more could do so in coming days, as Congress reconvenes.

And director Rob Reiner, who has helped organise glitzy Hollywood fundraisers for Mr Biden in the past, posted on X, formerly Twitter: “It’s time for Joe Biden to step down.”

Meeting in person will give congressional Democrats a chance to discuss concerns about Mr Biden’s ability to withstand the remaining four months of the campaign — not to mention four more years in the White House — and true prospects of beating former Republican former president Donald Trump.

The president’s campaign has announced a 50 million-dollar (£39 million) ad blitz throughout the month meant to target large-audience moments such as the upcoming Olympics in Paris. Still, Mr Biden’s campaign team is quietly bracing for the chorus of those calling for him to leave the race to grow in coming days — holding the call with surrogates and calling and texting politicians to try to head off more potential defections.

Mr Biden got a weekend boost from other key Democrats who had raised previous questions but now have moved to support him, led by Speaker Emerita Nancy Pelosi and Representative James Clyburn of South Carolina. Still, with the Democratic convention approaching, the short term is especially critical.

Since his disastrous debate performance late last month donors, strategists, politicians and their constituents have urged Democrats to replace him at the top of the ticket before, they argue, it is too late. Mr Biden’s interview on Friday with ABC has not convinced some who remain sceptical that he can resurrect his campaign.

Appearing on CNN on Sunday, Democratic Senator Chris Murphy of Connecticut said that Mr Biden “needs to answer those questions that voters have”. But he added: “If he does that this week, I think he will be in a very good position and we can get back to what this campaign needs to be.”

Mr Murphy also said he did not know if a cognitive test “would be impactful” for voters worried about Mr Biden’s potential decline. During his Friday interview, Mr Biden rejected undergoing such testing, arguing that the everyday rigours of the presidency were proof enough of his mental acuity.

But California Democratic Representative Adam Schiff told NBC that he would be “happy if both the president and Donald Trump took a cognitive test”. Mr Trump, during his own campaign rallies, has said Mr Biden should undergo such testing while boasting about his own mental and physical stamina.

Mr Schiff added that the president opting to stay in the race “is going to come down to what Joe Biden thinks is best” and that he could “run hard” to beat Mr Trump or “if his decision is to pass the torch, then the president should do everything in his power to make that other candidate successful.”

Mr Biden has insisted he is not yielding to any other Democrat, saying he is the Democrats’ best shot to beat Mr Trump. His visit to a black church gives him a chance to energise African-American voters, who are Democrats’ largest and most loyal bloc of support.

It could also send a message to members of the Congressional Black Caucus, whose endorsement the president will need as he works to quell potential rebellion on Capitol Hill.

At the Essence Festival of Culture in New Orleans on Saturday, Mr Biden got enthusiastic support from four of the caucus’s members, including Representative Joyce Beatty, of Ohio, who told attendees “don’t get out there and turn your back on this president.”

California Democratic Representative Maxine Waters, who is 85, drew a standing ovation by declaring: “People say Joe Biden’s too old. Hell, I’m older than Biden!”

“It ain’t gonna be no other Democratic candidate,” Ms Waters said, “and we better know it.”