History question for you: in more than two centuries, how many incumbent US presidents have lost an election, and then won the White House again afterwards?
The answer is one. His name was Grover Cleveland, and he died in 1908.
Donald Trump has a chance to become the second.
We're obviously a long way out from the 2024 election, but Trump has already made it clear he wants to be president again.
Privately, he has reportedly been telling allies he expects to be "reinstated" before the end of 2021. That is not going to happen.
But nothing is stopping Trump from seeking the presidency again in 2024. And if he were to reach that goal, it would be an incredibly rare achievement.
Here's everything you need to know about that potential run.
Can Trump run for president again?
Absolutely. Under the US Constitution, anyone who is 35 or older, a natural born citizen of the country, and a resident for at least 14 years can run for president.
The 22nd Amendment limits presidents to two terms in office, but since Trump has only served one term, that's not an issue here.
What has to happen first?
Trump would need to win the Republican Party's presidential nomination.
The nominee is decided through a primary process. Whoever wants to represent the party campaigns for the nomination, and Republican voters choose the candidate they prefer.
At the moment, the polling is very clear: almost half of Republicans say they would choose Trump. His nearest rival, former vice president Mike Pence, is stuck in the teens. If he does run, he will be the overwhelming favourite.
What has Trump said about running again?
Trump has always liked to play coy about his future plans – he's big on building suspense – but all indications are he's leaning towards running.
Speaking to his daughter-in-law Lara Trump in March, Trump said his supporters "do have hope" that he'll seek the White House in 2024.
In an interview with Fox Business in late April, he said he was "100 per cent thinking about running again".
In May, he told talk show host Candace Owens he looked forward "to doing an announcement at the right time".
"It's very early. But I think people are going to be very, very happy when I make a certain announcement," said Trump, telling listeners to "stay tuned".
In June, reacting to Facebook's decision to ban him until at least 2023, he said the company's CEO Mark Zuckerberg would get no more cushy dinners "next time I'm in the White House".
For there to be a "next time", he'll obviously need to run again.
Who else will seek the Republican nomination?
If Trump does indeed run, there's every chance no one of note will oppose him. That's what happened in 2020.
But he was an incumbent president at that point, and incumbents rarely get challenged for their party's nomination. This time might be different.
So who are the potential contenders?
Pence, who served as Trump's loyal vice president for four years, might have a go – though he has fallen out of favour with many Republicans since he refused to unilaterally (and illegally) overturn Trump's defeat to Joe Biden.
How out of favour? Well, some of the rioters who stormed the Capitol on January 6 were heard chanting "hang Mike Pence". That gives you an idea.
Florida Governor Ron DeSantis would be an immediate top-tier candidate, having won admiration among Republicans for his handling of the coronavirus, which focused on keeping the state's economy as open and unrestricted as possible.
South Dakota Governor Kristi Noem was another leader sceptical of Covid restrictions, and she has a national profile.
On the more moderate side of the party, former South Carolina governor and United Nations ambassador Nikki Haley is often spoken of as a potential presidential candidate, though she has invited ridicule by repeatedly flip-flopping on her support for Trump.
Pro-Trump senators like Ted Cruz, Rand Paul and Josh Hawley have obvious presidential ambitions. Cruz and Paul ran against Trump for the Republican nomination in 2016, and failed, though Cruz did get second place.
Should Trump stay out of the race, his son Donald Jr might think about a bid.
And among the few remaining anti-Trump Republicans, Congresswoman Liz Cheney is probably the most likely to attempt a challenge.
What about those criminal investigations?
Trump is currently facing a couple of criminal investigations, one focusing on the finances of the Trump Organisation, and another zeroing in on his clumsy attempts to pressure election officials into overturning his defeat to Biden in Georgia.
These investigations might lead nowhere. But what if they don't? Say Trump is prosecuted. Say he is convicted.
None of this would stop him from running in 2024. Naturally, a criminal case or conviction would make it harder to win public support, but he could still legally enter the race.
How old will Trump be in 2024?
He'll be 78, the same age Joe Biden is now.
Both of these guys are notably old by historical standards. Trump was the oldest president ever elected to a first term when he took office in 2016, edging out Ronald Reagan. Biden is the oldest ever elected full stop.
Who would face Trump in the general election?
Biden's age is a factor here. He'll be just a couple of weeks short of his 82nd birthday when the 2024 election is held, almost a decade older than Reagan was when he won re-election in 1984.
The President insists he intends to run again.
"My plan is to run for re-election. That's my expectation," he said in March.
Say he doesn't, though. In that case, Vice President Kamala Harris would be the obvious favourite for the Democratic Party's nomination.
Before running for president herself in 2020, and losing to Biden, Harris was a US senator representing California. Before that, she was the state's attorney general.
She is broadly seen as a more progressive politician than Biden.
How many beaten presidents have come back to win again?
Just one, as we mentioned right at the top.
Grover Cleveland, a Democrat, won power in 1884 and then lost it to Republican Benjamin Harrison four years later.
He returned to his work in the private sector as a lawyer in New York. But Cleveland re-entered politics ahead of the 1892 election, and ended up getting his revenge on Harrison.
Three other presidents have tried to regain the White House after losing elections as the incumbent: Martin Van Buren, Millard Fillmore and Herbert Hoover.
None of them succeeded.