Joe Biden's withdrawal from the US presidential race has left Democrats in a precarious and chaotic position.
In just a few weeks at the party's national convention in Chicago, they were set to formalise him as their nominee for the November election.
It should have been straightforward, as Biden had secured a vast majority of party delegates to back him to run for a second term.
Those plans have been thrown into disarray, with the president pulling out of the race following weeks of scrutiny and pressure from his halting debate performance against Donald Trump in June.
Biden had 3,896 pledged delegates of the nearly 4,000 available, according to the election analysts at Associated Press.
By leaving the race, Biden has released all the pledged delegates he'd accumulated during the primary process earlier this year.
They are now free to choose a new candidate.
Biden has endorsed his Vice-President, Kamala Harris, as his successor — but he can't force his delegates to vote for anyone.
The key questions now are whether any other Democrats enter the race.
His withdrawal, amid widespread concerns about his age and ability, has fended off the unlikely, but more embarrassing scenario of an open revolt of his pledged delegates.
But a floor fight could get ugly.
"There could be literal chaos in Chicago … on the floor of the convention at the United Center," said Suzanne Chod, a professor of political science at Illinois's North Central College.
Who will replace Biden?
Joe Biden's choice is Vice-President Kamala Harris.
Many Democrats expressed support for the 59-year-old as the discourse around Biden's future intensified.
She has a cleaner path to legally inherit the original campaign's all-important fundraising as the second name on the Biden-Harris ticket.
Polling by CNN early in the week after the debate showed Harris performing strongly against Trump.
But many see her record in government as uneven.
"If Kamala Harris were viewed in the Democratic party as a sort of overwhelmingly popular figure that everybody just couldn't wait for her to be president in the next cycle, then this would be kind of easy," said Hans Noel, associate professor of government at Georgetown University.
"There's a lot of people who like Harris. There's also a lot of people who are disappointed and would rather have somebody other than someone who was one of the options in 2020 and dropped out."
If not Harris then who?
That could mean an open convention, where the party nominee is selected at the convention itself, a process that hasn't been seen since 1968.
Were that the case, a new candidate would need a simple majority of delegates to become the nominee.
If a first round of voting failed to decide a nominee, a second round would be held where 700 "superdelegates" vote.
Superdelegates tend to be senior Democratic party leaders.
Their entry into the ballot gives candidates 700 more opportunities to build a majority – and because they tend to be influential voices within the party, they can also help sway the original batch of delegates.
There are plenty of names that have been in the mix.
Democratic governors like Gretchen Whitmer in Michigan, Gavin Newsom from California, the Illinois billionaire JB Pritzker and Kentucky's Andy Beshear have all been mentioned.
Pennsylvania Governor Josh Shapiro has been seen as a strong performer after winning office in the key swing state in 2023.
Pete Buttigieg, who also ran in 2020, has spent the last four years in a partial spotlight as Biden's Transportation Secretary.
There have been other names tossed around too, though they're probably longer odds: Maryland's Governor Wes Moore, or senators Amy Klobuchar (Minnesota), Cory Booker (New Jersey), Mark Kelly (Arizona) or Raphael Warnock (Georgia).
The youngest in this group are Governors Beshear and Moore, respectively 46 and 45 years old.
The oldest is Klobuchar, at 64 — that's still 17 years younger than Biden.
Then there's the wildcard option from outside the party.
Independent candidate Robert Francis Kennedy Jr, known widely as RFK Jr, suggested on a podcast before Biden left the race that the "best choice" would be for him to step in as the Democratic nominee.
But confirming the top of the ticket is only one step in the process.
If Kamala Harris does become the nominee, she'll also need to pick a running mate.
How messy could this become?
The historical examples aren't likely to fill the Democrats with confidence.
The last open convention was in 1968 — a year so messy it prompted the Democratic party to change its rules.
This year the Democrats had been planning a virtual "roll call" ahead of their August convention, which would have confirmed Biden even before the party gathered in Chicago.
It's not clear if that roll call will go ahead now.
Either way, the path ahead is likely to be tumultuous.
"The nominating process, during the primary and at a convention — because each state has its own rules — is very, very complicated," Professor Chod said.
"The idea there's a grand sweeping way to do this quickly, to replace Biden quickly and quietly — those are not options.
"It would be public, it would be loud, it would be messy."
There's also the risk it could be seen by voters as somewhat undemocratic, she added.
Professor Chod said it also risked playing right into Republican talking points that everything the Democratic Party does is "rigged, fraudulent and not democratic".
"What we know is that the more stable and cohesive the nominating process is, the better chance that candidate has of winning an election," she said.
Is Joe Biden still president?
Biden is no longer the party's nominee to contest the November election, but remains president until his successor's inauguration in January 2025.
That gives him about six months left in office, though he risks looking like a lame duck.
There is a mechanism in the US constitution for the vice-president and the majority of the cabinet to declare the president unfit for office.
It's called the 25th amendment.
It's never been used, though Democrats wanted then-vice-president Mike Pence to invoke it against Trump after the January 6 riot at the US Capitol in 2021, but he refused.
If Biden's cabinet was to take such an extraordinary step, power would be transferred to the vice-president to serve as acting president until January.
But no-one working for Biden has indicated that invoking the 25th amendment is necessary.
"I am so proud to serve under his leadership, and thankful for his unwavering focus on what is best for our country," Buttigieg said.
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