President Biden and former President Donald Trump are scheduled to face off on the debate stage on Thursday for the first time in four years.

And while the picture of the two candidates behind the podiums may look pretty much the same as it did in 2020, much has changed since then.

To name a few: Biden is running as an incumbent; Trump is fresh off a historic criminal conviction. The COVID-19 public health emergency is technically over. And the terms and format of the debate itself are brand new.

Biden and Trump agreed this spring to a pair of presidential debates hosted by TV networks in June and September, in a pointed departure from the traditional schedule and process of the Commission on Presidential Debates.

Thursday’s is hosted by CNN at its Atlanta studio, without an in-person audience and governed by a new set of rules.

Those include the addition of two commercial breaks, points out Mary Kate Cary, formerly a speechwriter for President George H.W. Bush.

“They’re not allowed to talk to their staff during the commercial breaks, and the microphones will be muted when the other person is speaking,” told NPR’s Morning Edition. “And I think that’s going to be a big contrast to the last time these two had a first debate, in 2020.”

Their first on-stage matchup in September 2020 was dominated by Trump’s repeated interruptions and refusal to condemn white supremacists, and was widely criticized by viewers and commentators alike.

One COVID-canceled debate and some rule changes later, the two reunited for a final, less chaotic faceoff in October — at which point tens of millions of Americans had already cast their votes.

With Trump and Biden now near even in the latest polls, and many Americans unenthused — and still undecided — about voting for either of them, Thursday’s debate offers both candidates an opportunity. But it’s not without risks.

It’s likely to be a memorable night if 2020 is any indication. Here’s a look at what happened last time Trump and Biden took the stage together.

1. Trump derailed the first debate

The first round, in September 2020, was by many accounts a disaster. NPR’s Domenico Montanaro called it “maybe the worst presidential debate in American history.”

Trump arrived on the debate stage trailing in the polls and, apparently, jonesing for drama. He interrupted Biden constantly, peppering him with questions and personal slights despite moderator Chris Wallace’s pleas for order.

At one point, while Biden was talking about his late son Beau’s military service, Trump jumped in to attack his other son, Hunter, for his drug use (which Biden managed to seize as a sympathetic moment).

Biden tried in vain to ignore Trump talking over him throughout — but called the then-president a “clown” more than once. At one point he had clearly had enough.

“Will you shut up, man?” he said exasperatedly, as Trump continued accusing him of wanting to pack the Supreme Court. “This is so unpresidential.”

Trump even bulldozed over Wallace, prompting the then-Fox News anchor to declare, “Mr. President, I am the moderator of this debate and I would like you to let me ask my question and then you can answer.”

Still, a few substantive moments stood out amidst the chaos and crosstalk.

One was when Wallace asked if Trump was willing to condemn white supremacists and tell them to “stand down.”

Trump blamed the “left-wing” instead, but said he was prepared to do so. At that point, both Wallace and Biden urged him to go ahead. Trump asked for a name, and Biden suggested the Proud Boys.

“Proud Boys, stand back and stand by,” Trump said, in what sounded more like a call to action, and quickly became part of the far-right extremist group’s new social media logo.

Trump also repeatedly made baseless claims about the upcoming election being rigged, saying “This is going to be fraud like you’ve never heard.”

When Wallace asked if he would urge his supporters to stay calm during a potentially prolonged period of counting ballots, Trump demurred. He said instead that he was “urging my supporters to go into the polls and watch very carefully.”

“If it’s a fair election, I am 100% on board,” he said. “But if I see tens of thousands of ballots being manipulated, I can’t go along with that.”

Trump was wrong about widespread fraud. But his other comments turned out to be a bit of foreshadowing, as the former president has since been charged with multiple felony counts for attempting to overturn the election and disrupt the peaceful transfer of power.

2. The second debate was scrapped over COVID concerns

Their next debate, scheduled for Oct. 15 in Miami, was scrapped altogether due to disagreement between the campaigns and the Commission on Presidential Debates over COVID-19 protocols.

Trump refused to debate virtually after he was diagnosed with the virus himself.

Trump announced on Oct. 2 that he and First Lady Melania Trump had tested positive for COVID-19.

Later that day he was airlifted to Walter Reed, where he remained for the next three days, receiving experimental treatments as the country waited for updates and the White House seemingly struggled to explain the timeline of his previous exposures and public engagements.

At the time, questions were mounting about whether Trump had taken a test (as required by the debate commission’s “honor code” system) — and gotten a positive result — before his first debate with Biden. It later became apparent that he had: His former Chief of Staff Mark Meadows wrote in his 2021 book that Trump tested positive for COVID-19 three days before that first debate.

On Oct, 8, the commission announced it would shift to a virtual debate due to health and safety concerns. Trump’s team countered that he would be cleared for public events by then, saying there was “no medical reason” why the debate couldn’t be held in person.

Trump ultimately pulled out of the virtual debate, calling it “a waste of time.”

After more back and forth (Trump’s team proposed delaying the second and third debates by a week; Biden rejected that idea), the commission canceled the debate altogether, less than a week in advance.

Instead, each candidate held individual town halls — Trump on NBC News, Biden on ABC News — on Oct. 15, both airing at the same time.

3. The final debate was less dramatic

Trump and Biden returned to the debate stage in Nashville on Oct. 22, less than two weeks before Election Day.

By that point, more than 40 million Americans had already cast their votes by mail, Biden held a 10-point lead in an average of national polls and only a small sliver of voters appeared willing to be persuaded.

The debate proved much less dramatic than the first round, partly due to new rules that kept each candidate’s microphone muted during the first two minutes of their opponent’s speaking time, and the no-nonsense approach of moderator Kristen Welker of NBC News.

Montanaro wrote, “Even Biden appeared bored, and near the end of the debate checked his watch.”

Both candidates were relatively restrained on the issues — COVID, healthcare and the economy.

But things got testy when the two sparred over personal finances. Trump claimed Biden made money from Russia, China and Ukraine, which Biden denied before blasting Trump for refusing to release his income tax returns.

Continuing his line of attack, Trump sought to paint Biden as a typical (and corrupt) politician.

“I’m not a typical politician,” Biden returned. “That’s why I got elected.”

4. VP bonus round: Pence, Harris and a pesky fly

Vice President Mike Pence and then-Sen. Kamala Harris squared off in a debate of their own in early October, during Trump’s COVID convalescence and as the fate of the subsequent presidential debates hung in the balance.

While the VP debate was never likely to shift the election, it highlighted sharp contrasts between Democrats’ and Republicans’ agendas on topics like the pandemic, health care and the economy.

Both candidates did their share of shirking follow-up questions, and Harris called out Pence — “Mr. Vice President, I’m speaking” — when he started to step on her time.

The most memorable takeaway from the night, however, wasn’t what the candidates did or did not say, but who else joined them onstage.

A fly landed on Pence’s white hair and lingered for a solid two minutes as he continued speaking, seemingly unaware. Within minutes of the debate’s end, the Biden campaign tweeted out a fly-swatter-themed donation pitch.

This time around, Trump has not yet announced his VP pick, though has done a lot of hinting that he knows who it will be.

It’s unclear whether Trump’s eventual running mate will also wind up on the debate stage — but CBS News reported last month that Harris had accepted its invitation for a debate, either on July 23 or Aug. 13.