For both, it could be a chance to change — or cement — the trajectory of a campaign that has remained surprisingly stable despite foreign policy crises, ongoing criminal cases and the first felony conviction of a U.S. president.

With tens of millions of Americans expected to tune into the earliest presidential debate in history, the showdown will allow an increasingly pessimistic electorate to evaluate the two men for themselves.

It will be held inside CNN’s midtown Atlanta studios without a live studio audience at 9 p.m. and be simulcast on most major network and cable channels. Here are key factors to watch:

How do both handle doubts about their health?

The oldest candidates ever to compete in a presidential race, Biden and Trump have both faced questions about their mental and physical abilities.

How will Trump’s criminal troubles factor?

The legal challenges facing Trump in Atlanta and other jurisdictions are sure to be a topic.

The Republican was convicted by a New York jury in May of 34 felony charges in a scheme to conceal an alleged affair with a porn star.

Biden, however, has been reluctant to lean into the criminal record over fears it could galvanize the GOP base.

An Atlanta Journal-Constitution poll released this week shows how divisive the criminal charges are. Nearly half of all voters polled say they approve of the New York jury’s May verdict, including a bare majority of independent voters. And roughly one-third of independents polled say the convictions make them less likely to back Trump.

But an overwhelming majority of Republicans disagree with the verdict, and Trump’s message that the charges are the byproduct of a weaponized political justice system has seeped deep into the party’s base. Still pending are racketeering charges against Trump and 14 co-defendants over his efforts to reverse his 2020 defeat, a case that could go to trial as early as 2025.

“What they put this man through is unbelievable,” Republican state Sen. Brandon Beach said. “It’s election interference.”

Will Trump erupt?

The debate may be remembered more for what Biden gets Trump to say than what the president himself says.

Their first debate in 2020 was marred by a string of outbursts and interruptions by Trump that rendered parts of the showdown unwatchable — and helped Biden project an aura of command.

Biden will likely try to paint a second Trump administration as more chaotic than the first. Republicans hope Trump steers clear of any explosive exchanges with Biden that paint him as out-of-touch.

“I hope he stays focused on immigration and the economy — and then lets Joe Biden have to defend himself,” said former Republican U.S. Rep. Doug Collins, a Trump ally. “Sitting presidents aren’t used to getting questioned, and this president in particular isn’t used to it.”

Duncan put it a different way: “We are going to see if Donald Trump has all of the sudden mysteriously found discipline.”

Will it have a lasting impact?

Sometimes, debates become a turning point in campaigns. Sometimes, they’re hardly remembered. We’ll know soon whether the Atlanta showdown has a place in history or is just a footnote.

Fred Hicks, a veteran political strategist, outlined the challenges for both men:

Biden must find a way to entice Black men and younger voters back to the polls through “fire and inspiration.”

Trump needs to woo mainstream Republicans and centrists, including those who backed former South Carolina Gov. Nikki Haley’s presidential bid, to put aside their concerns and rally to him.

“Both of these are tall tasks,” he said. “And this debate will be their most challenging test yet.”