Millions of eyeballs will be on Thursday's debate -- here's what to watch for as Biden and Trump face off.

Will any gaffes or knockout punches break through? Conversations on policy are unlikely to break through, but viewers could remember a serious lapse or a zinger that lands.

Will character or policy rule the day? Both sides have lobbed personal attacks -- Biden has dubbed Trump a "convicted felon" and threat to democracy, and Trump has essentially called the president, without evidence, the leader of a crime syndicate. Will the debate stay focused on issues like abortion, immigration and the economy? Or will the two candidates opt for a more scorched-Earth stance?

Typically, a sitting president is debating a governor or senator, with the incumbent's record the main focus. But Trump also spent four years in the White House. Whose record will get more scrutiny?

The debate is happening uniquely early in an election cycle. It remains unclear if any big moments will be washed away by November, or if it'll help set the tone heading into the summer.

The debate is also featuring a novel format -- microphones will be cut off when candidates aren't recognized to speak, and there will be no audience to feed off of. That could deprive Trump of the energy he seeks, helping Biden. But the microphone cutoffs could help "enforce some discipline" on Trump, said GOP strategist David Kochel.

Read more here.

Hi everyone, I'm Aaron Sharockman, the executive director of PolitiFact. I'm excited to join the ABC/538 team to provide fact-checking of the candidates. If you don't know PolitiFact, we've been fact-checking political statements since 2007 using our Truth-O-Meter, which rates claims on a scale from True to Pants on Fire False.

We'll be providing you real-time updates throughout the night.

How? Well, it's not because we're super smart or super fast (though maybe we are a little bit). No, it's really because we've been fact-checking Biden and Trump for more than a dozen years. And over all those years, and all their campaigns, they've said a lot of things worth fact-checking.

And both candidates often repeat themselves.

Our team of 25 fact-checkers and editors have prepped dozens of instant fact-checks based on what we expect Trump and Biden might say. And if they do, we'll be able to share that analysis with you almost instantly.

If you want a primer of what we expect to hear tonight -- and how accurate those claims are -- you can take a look here.

-Analysis by Aaron Sharockman, PolitiFact

Heading into tonight's event, Biden and Trump are locked in a close contest. 538's presidential election forecast rates the race as a dead heat, with both Biden and Trump having about a 1 in 2 shot of winning the election. This falls in line with our national polling average, which has the two candidates just about tied at 41%, with Kennedy polling at 9%.

But as readers know, U.S. presidential elections aren't decided by the national popular vote. Instead, they're decided by the Electoral College, where the results in individual states determine who wins each state's electoral votes, with a majority of 270 out of 538 in total necessary to claim victory. Currently, the forecast shows an extremely tight race in each of the most pivotal states.

For instance, Biden's path to victory may rest primarily on winning the Frost Belt battlegrounds of Michigan, Pennsylvania and Wisconsin that he carried in 2020. While the forecast shows him with small leads in each of those states, Biden's advantage is well inside the range of potential outcomes, meaning Trump could easily carry them once we get to November. Meanwhile, Trump holds a narrow edge in the Sun Belt swing states of Arizona, Georgia, Nevada and North Carolina, but similarly his leads are far from secure.

Still, with nearly four months to go until Election Day, there's a great deal of uncertainty around where public opinion will stand when voters cast their ballots. 538's forecast utilizes a combination of polling information and campaign fundamentals, such as the economic situation and each state's partisan leanings. Together, those indicators show a toss-up race that could go in either direction.

Now, tonight's debate could move the contest: Historically, the margin in presidential races has shifted by an average of about 2 points in the two weeks following the first general election debate in cycles dating back to 1976. In what could be bad news for Biden, that movement has more often than not gone against the incumbent president or party. Yet we're still sailing in uncharted waters. After all, this election involves both a sitting and former president, an unprecedented matchup in modern times. The debate is history-making, too: It's nearly three months earlier than any past general election face-off.

-538's Geoffrey Skelley

Hours before the debate, first lady Jill Biden told deep-pocked donors that the president is "ready" for his faceoff against Trump.

"Joe's ready to go. He's prepared. He's confident," she said at a fundraising retreat at the Ritz-Carlton in downtown Atlanta, according to the press pool. "You know what a great debater he is."

She thanked donors for "making the right choice" for democracy, urging them to keep up their work in support of Biden, according to the press pool.

"We can't stop now. We can't get complacent," the first lady said. "We've got to keep working together, working harder than we've ever worked before."

-ABC News' Fritz Farrow, Gabriella Abdul-Hakim and Will McDuffie

During the debate, Trump claimed that Democrats "support abortion up to and even beyond the ninth month," and contended that some Democratic states have had such a stance.

Democrats have never advocated for killing a baby after it is born as this would be murder, which is illegal in every state. Nine states have no abortion restrictions in place; however, it should be noted that late-term abortions are exceedingly rare, representing 1%, according to KFF.