A press conference in which Joe Biden described Kamala Harris as "Vice President Trump" has only amplified pressure on him to drop out of the race.
The president made several concerning gaffes, including mistaking Ukrainian President Volodymyr Zelenskyy for Russian leader Vladimir Putin.
And soon after, his first press conference in months did little to assuage the concerns of his party members.
Minutes after the press conference, two Democratic congressmen called for him to drop out.
"The stakes are high, and we are on a losing course," Rep. Scott Peters said in a statement.
And Rep. Jim Himes said Biden staying on would risk throwing the election to Donald Trump.
"He must not risk that legacy, those accomplishments and American democracy to soldier on in the face of the horrors promised by Donald Trump," he said.
But a presidential candidate dropping out of the race after securing the nomination is unprecedented.
If Biden drops out, it creates many questions that need to be answered.
Will Joe Biden drop out?
If the president has decided to withdraw, he hasn't indicated so publicly.
Instead, he appears resolute on staying in the race.
"If the Lord Almighty came down and said, 'Joe, get out of the race,' I'd get out of the race," Biden said on Friday.
"The Lord Almighty's not coming down."
But politicians rarely flag they are going to quit until the moment they do.
It's possible Biden is getting all his ducks in a row, so to speak, lining up a successor and preparing to step aside.
But senior Democrats' increasingly frustrated remarks about the president seem to indicate that Biden wants to stay put.
Can Joe Biden beat Donald Trump?
Biden's numbers weren't great before the debate, and have dropped precipitously since then.
Trump meanwhile has been found guilty of 34 criminal charges and is facing dozens more across three other elections - and yet he is leading in the polls.
What makes Democrats particularly antsy is that polling shows almost every other potential candidate is in a winning position against Trump.
What will happen if Joe Biden drops out?
The process to select a presidential nominee is very complicated.
The primary elections in each state are officially to select delegates to the national convention, which is scheduled for mid-August.
Having won every state primary in a landslide, most of those 4521 delegates are pledged for Biden - people his campaign picked so they would support him.
If Biden decides to stay in the race, most of those delegates are bound to vote for him at the convention.
But if he withdraws his name, those delegates will be free to vote for whoever they want.
Potential candidates would then put up their hands to try and win over a simple majority of delegates.
This is actually how presidential nominees were selected before 1968, but the mess of that year led to the parties changing to the current system.
Complicating the process is a deadline for getting on the ballot in the state of Ohio.
Because the deadline takes place before the actual convention, delegates were due to officially nominate Biden in late July.
The convention would then be a public display of support after the paperwork had already been submitted.
Will Kamala Harris replace Joe Biden?
Delegates can vote for whoever they like, but the likely replacement would be Vice President Kamala Harris.
Harris is not especially popular with voters, but she has built-in advantages.
Because the money raised is for the Biden-Harris ticket, that war chest would remain in the campaign's hands.
Other candidates would have to start the potentially billion-dollar run without it.
She's also been vetted by the notoriously nosy Washington press.
Because she's already vice president, there's not likely to be any skeletons in her closet that voters don't already know about.
It would also be unpopular among Democrats' strongest demographic groups, African-Americans and women, to pass over the Black female vice president for someone else.
Who else could replace Joe Biden?
There's other Democrats who would be savouring the opportunity to jump into the race.
California Governor Gavin Newsom has been acting as a campaign surrogate for months, taking every opportunity to get his face on TV to espouse his party's values.
Newsom is charismatic and very much looks the part.
But California has a bad reputation in the crucial midwestern states, and he has become a liberal bogeyman to conservatives.
Michigan Governor Gretchen Whitmer is a less familiar option, but is increasingly being mentioned.
Delegates may be drawn to choosing the candidate who won a large swing state by a landslide when she was on the ballot in 2022.
The same could be said of Pennsylvania Governor Josh Shapiro, who has a very high approval rating in one of the most important states.
Meanwhile, Andy Beshear became a contender when he was re-elected governor of Kentucky last year, a stunning achievement for a Democrat in one of the most Republican states.
Transportation Secretary Pete Buttigieg was very impressive in his 2020 run, though would still be the youngest person ever elected president.
The name that always tops the wishlist is former First Lady Michelle Obama.
But unlike her husband, Obama says she loathes politics and would never accept the nomination.
What if Biden resigns the presidency?
If Biden drops out of the re-election race, he would remain president until January nevertheless.
But there's also talk of Biden quitting the presidency altogether out of concerns for his health.
In that case, Harris would be immediately elevated to the presidency.
That wouldn't automatically make her the nominee in November's election, but it would be hard to imagine someone else getting it.
Biden would be only the second president to resign, following Richard Nixon in 1974.
At the time, Biden was the youngest member of the Senate.
