PHILADELPHIA — President Biden on Sunday basked in warm applause of a Black congregation in Philadelphia, drawing support from a sanctuary of Black worshipers at a time of tumult and peril for his reelection efforts.

Biden attended a service at Mt. Airy Church of God in Christ in Philadelphia, in a swing state that will serve as a critical proving ground for his campaign reboot. Biden and his aides have insisted that he will not step aside as the Democratic nominee, ignoring a growing number of calls from Democrats for him to bow out after his halting debate performance.

Black voters have been a bedrock of political support for Biden throughout his presidential campaigns. He greeted the congregation by stating: “It’s good to be home.”

“We’re all imperfect beings,” Biden said in brief remarks. “We don’t know where or what fate will deliver us to or when. But we do know is that we can seek a life of light, hope, love and truth no matter what. We can seek that life.

“We have to work together,” the president added. “Because when we do, you can’t stop us.”

As he finished his remarks, the crowd chanted: “Four more years! Four more years!”

In recent days, even as party leaders express private concerns and a growing number of elected officials publicly call on him to drop out, it has been the Black community that has backed Biden most strenuously. From the start of the service, Pastor Louis Felton was emphatic in his support for Biden, urging worshipers to stand and shout, “We love you, President Biden!”

Biden stood and raised his hands during songs, and linked arms with the pastor next to him during prayer. Felton made a point of noting that the president was sitting next to a 91-year-old bishop, the founder of the church, Ernest C. Morris Sr.

“Don’t let anyone talk about your age. You’re a young whippersnapper,” Felton proclaimed.

The pastor also drew a clear contrast between Biden’s actions and a religious tie-in Donald Trump started in March, when he began selling a $60 Bible. “This president doesn’t sell the Bible. He actually reads the Bible.”

Amid rising unease among Democratic members of Congress and governors — who have largely remained publicly loyal to Biden — the president’s campaign aides scrambled to schedule Sunday’s events to show Biden’s vigor and his intention to forcefully confront Trump.

Earlier Sunday, Biden greeted Democratic Sens. Bob Casey and John Fetterman when he arrived in Pennsylvania. He spoke with each briefly, tapping Fetterman’s chest with his fist.

Later Sunday, Biden will travel to Harrisburg for a community organizing event with union members and local Democrats. Throughout the day, the president is expected to be joined by Pennsylvania Gov. Josh Shapiro and Lt. Gov. Austin Davis.

The appearances with the state’s two senators — and a later one with Shapiro, a rising Democratic star — are part of the campaign’s carefully orchestrated tableau to show that key figures in the party are standing behind the president. Biden’s 22-minute interview with George Stephanopoulos of ABC News, which aired Friday night, did little to change the restive mood of members of his party at a moment when he is sliding further behind in the polls and a majority of Americans say he is no longer fit to hold office.

Five congressional Democrats have called on Biden to drop out of the race, and at least 17 current and former top Democrats as of Saturday have publicly raised concerns about his fitness for office and his ability to defeat Trump. The latest to urge Biden to seek advice beyond his inner circle was Rep. Adam Schiff (D-Calif.), who is running for the Senate seat of the late Dianne Feinstein.

In a Sunday interview with NBC’s “Meet the Press,” Schiff said Biden’s debate performance “rightfully raised questions among the American people about whether the president has the vigor” to defeat Trump, adding his view that Biden “should be mopping the floor” with Trump.

“Joe Biden is running against a criminal. It should not be even close, and there’s only one reason it is close, and that’s the president’s age,” Schiff said. “He’s obviously talked to his family about this, and that’s important. But he should seek out people with some distance and objectivity.”

Schiff said Biden should be contemplating “whether he made the right decision to run or to pass the torch. That is the most important decision for him to make right now,” he said.

Sen. Chris Murphy (D-Conn.), a close ally of Biden, said on CNN’s “State of the Union” that the president would have to assuage voters’ concerns by showing them “whether this is still the old Joe Biden.” He did not directly answer a question about whether Biden should be his party’s nominee.

“I support Joe Biden. Period, stop,” Murphy said. “But I know that there are a lot of voters out there that need to be convinced that Thursday night’s debate performance was a bad night. … Ultimately, I’m supporting Joe Biden. I’m going to vote for Joe Biden. But the president needs millions of votes.”

On Friday, Biden repeatedly rebuffed questions from Stephanopoulos about whether he would undergo an independent medical evaluation that included neurological and cognitive tests, insisting that he gets “a full neurological test every day” simply by carrying out his presidential duties. Schiff said both Trump and Biden should undergo cognitive tests.

The next few days will be pivotal in determining whether Biden can maintain the confidence of his party as he and his campaign aides insist that his debate performance was an aberration rather than evidence of cognitive decline.

House Minority Leader Hakeem Jeffries (D-N.Y.) has scheduled a call Sunday afternoon with top House Democrats, in part to field concerns from members who are worried about the drag that Biden’s candidacy could have on down-ballot races.

Lawmakers are returning to Washington on Monday, gathering for the first time after the Fourth of July holiday as they weigh whether the party can prevail in the critical battle for control of the House and Senate in November with Biden as the Democratic Party’s nominee. Biden plans to return to the White House on Sunday night, ahead of this week’s NATO summit in Washington. On Thursday, he is planning to hold a rare solo news conference.

Biden’s campaign has also added a trip Friday to Michigan, according to a person familiar with the schedule, who spoke on the condition of anonymity to discuss events that had not yet been made public. It will be the third battleground state he has visited in a week.

First lady Jill Biden, who has been a constant presence on the campaign trail since the debate, is planning a three-city campaign swing Monday to Tampa; Wilmington, N.C.; and Columbus, Ga.

Reston reported from Washington. Azi Paybarah and Joby Warrick in Washington contributed to this report.