US President Joe Biden is looking forward to "getting back on the campaign trail next week", fortifying his commitment to stick in the race as more Democrats on Friday called for him to step aside as the party nominee.

“The stakes are high, and the choice is clear. Together, we will win," he said.

His statement appeared to be in response to the conflicting reports that Mr Biden's inner circle is discussing the beleaguered president's future and whether he will remain in the race.

Over the last several weeks, Mr Biden has been caught in a whirlwind of political pressure to step down: Calls from leaders within his own party to withdraw from the race, a loss of big-ticket donors and the added pressure that his decision could cost Democrats control of Congress.

At least a dozen Democratic lawmakers have called for him to step aside on Friday alone, and Vice-President Kamala Harris - considered the top choice to replace Mr Biden - was tasked with comforting worried donors on a Friday afternoon call.

Ms Harris said that she believed "in my heart of hearts" that "we are going to win this election", an individual who listened to the conversation told the BBC.

"We know which candidate in this election puts the American people first: Our president, Joe Biden," she added.

Earlier in the day, Mr Biden’s re-election campaign chair Jen O’Malley Dillon also attempted to push back on speculation that the president would withdraw in an appearance on MSNBC's Morning Joe

“Absolutely, the president’s in this race,” she said when asked about Mr Biden's plans.

She described him as "more committed than ever to beat Donald Trump" and said he's the "best person" to take on the former president.

In his statement, the president referenced former President Trump's Republican National Convention speech to say he will continue "exposing the threat" of the former president while "making the case" for his record.

"Donald Trump’s dark vision for the future is not who we are as Americans. Together, as a party and as a country, we can and will defeat him at the ballot box," he said.

As the conflict played on on Friday, the president was under quarantine at his home in Rehoboth Beach, Delaware. He tested positive for Covid-19 while traveling in Las Vegas earlier this week. Mr Biden is experiencing “mild symptoms”, the White House said.

Since his poor debate performance last month, Mr Biden has insisted he will continue to run, though his perspective on what it would take for him to step down as the Democratic nominee has evolved.

First telling ABC News' George Stephanopoulos "only the Lord Almighty" would make him stand down, Mr Biden said this week during an interview with BET (Black Entertainment Television) that he would re-evaluate the campaign if a doctor told him he had a serious medical condition.

According to a campaign memo released on Friday, Mr Biden isn't going anywhere.

"Joe Biden has made it more than clear: He’s in this race and he’s in it to win it," according to the memo. "Moreover, he’s the presumptive nominee — there is no plan for an alternative nominee. In a few short weeks, Joe Biden will be the official nominee. It is high past time we stop fighting one another. The only person who wins when we fight is Donald Trump."

Time is running out for Mr Biden to decide if he will step down.

The Democratic National Convention begins 19 August, but the Democratic National Committee is expected to meet virtually the first week of August to nominate Biden as the official party nominee to meet state ballot deadlines.

The DNC rules committee met on Friday morning to discuss the procedures for the virtual roll-call vote, which they intend to hold before 7 August.

When asked whether another candidate could challenge Mr Biden in the roll-call vote, the committee's co-chair Leah Daughtry said that "any challenger would have to have the verified support of hundreds of delegates".

With Mr Biden winning nearly all of the available delegates during the Democratic primary, that requirement would be nearly insurmountable.

Ms Daughtry noted that "such a challenge has never happened over the past half century of competitive primaries".

The pressure continues to build, however.

On Friday, Democratic Senator Martin Heinrich, of New Mexico, became the third Democrat in the upper chamber to call for Biden to step aside.

"By passing the torch, he would secure his legacy as one of our nation's greatest leaders and allow us to united behind a candidate who can best defeat Donald Trump and safeguard the future of our democracy," he wrote in a statement on X, formerly Twitter.

His statement follows that of Democratic Senator Jon Tester, of Montana, who called on Biden to end his re-election bid on Thursday.

"While I appreciate his commitment to public service and our country, I believe President Biden should not seek re-election to another term," Mr Tester wrote in a statement on X.

In the House, Congressman Jim Costa, a Democrat from California, also called for him to withdraw on Thursday.

Democratic congressmen Jared Huffman of California, Marc Veasey of Texas, Chuy Garcia of Illinois and Mark Pocan of Wisconsin released a joint message on Friday saying "the most responsible and patriotic thing" Biden could do is "step aside as our nominee".

"With great admiration for you personally, sincere respect for your decades of public service and patriotic leadership, and deep appreciation for everything we have accomplished together during your presidency, it is now time for you to pass the torch to a new generation of Democratic leaders," they wrote in the joint statement.

Illinois Democratic congressman Sean Casten wrote in the Chicago Tribune on Friday that he doesn't think the president can defeat former US President Donald Trump.

"It is with a heavy heart and much personal reflection that I am therefore calling on Biden to pass the torch to a new generation," he wrote.

Other members of the House joined the calls for the president to step aside on Friday, including Zoe Lofgren of California, Kathy Castor of Florida, Morgan McGarvey of Kentucky, Greg Landsman of Ohio and Betty McCollum of Minnesota.

Reports this week suggested senior Democratic leaders are leaning in the same direction.

Senate Majority Leader Chuck Schumer, House Minority Leader Hakeem Jeffries and former House Speaker Nancy Pelosi have all reportedly expressed concerns during private conversations with Mr Biden about his candidacy. In public statements, Ms Pelosi's staff insisted her comments have been misrepresented and Mr Jeffries affirmed his support for Mr Biden.

Former President Barack Obama, Mr Biden's previous running mate, has reportedly said Mr Biden's chances of winning the election have greatly diminished.

Lawmakers haven't been the only ones turning their backs to Biden. Big name donors - including actor George Clooney and Disney family heiress Abigail Disney - have closed their wallets.

Despite the defectors, some are sticking by his side.

New York Rep. Alexandria Ocasio-Cortez, one of the most influential progressive voices in the House, has supported Biden over the last few weeks. She broadcast live on Instagram on Friday morning and spoke about the risks of entering the convention without Biden as the presumptive nominee, including potential legal challenges and ballot access deadlines.

The Congressional Hispanic Caucus, which has about 40 members, and the 60-member Congressional Black Caucus, have both met with the president and also indicated their support for his re-election bid.