Washington. It's Election Day. Polls opened Tuesday across the nation and Americans cast ballots in the 2024 presidential election. In a deeply divided nation, the election is a true toss-up between Democrat Kamala Harris and Republican Donald Trump.

We know there are seven battleground states that will decide the outcome, barring a major surprise. But major questions persist about the timing of the results, the makeup of the electorate, the influx of misinformation — even the possibility of political violence. At the same time, both sides are prepared for a protracted legal battle that could complicate things further.

Here's what to watch on Election Day 2024:

History will be made either way
Given all the twists and turns in recent months, it's easy to overlook the historical significance of this election.

Harris would become the first female president in the United States' 248-year history. If elected, she would also be the first Black woman and person of South Asian descent to hold the office. Harris and her campaign have largely played down gender and race, fearing that they might alienate some supporters. But the significance of a Harris win would not be lost on historians.

A Trump victory would represent a different kind of historical accomplishment. He would become the first person convicted of a felony elected to the U.S. presidency, having been convicted of 34 felony counts in a New York hush-money case little more than five months ago.

Trump, who is still facing felony charges in at least two separate criminal cases, argued that he is the victim of a politicized justice system. And tens of millions of voters apparently believe him — or they're willing to overlook his extraordinary legal baggage.

How long will it take to know the winner?
Election Day in the United States is now often considered election week as each state follows its own rules and practices for counting ballots — not to mention the legal challenges — that can delay the results. But the truth is, nobody knows how long it will take for the winner to be announced this time.

In 2020, The Associated Press declared President Joe Biden the winner on Saturday afternoon — four days after polls closed. But even then, The AP called North Carolina for Trump 10 days after Election Day and Georgia for Biden 16 days later after hand recounts. Four years earlier, the 2016 election was decided just hours after most polls closed. The AP declared Trump the winner on election night at 2:29 a.m. (it was technically Wednesday morning on the East Coast).

This time, both campaigns believe the race is extremely close across the seven swing states that are expected to decide the election, barring a major surprise: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin. The size of the map and the tightness of the race make it hard to predict when a winner could be declared.

Where can I find early clues about how the contest might unfold?
Look to two East Coast battleground states, North Carolina and Georgia, where the results could come in relatively quickly. That doesn't mean we'll get the final results in those states quickly if the returns are close, but they are the first swing states that might offer a sense of what kind of night we're in for.

To go deeper, look to urban and suburban areas in the industrial North and Southeast, where Democrats have made gains since 2020.

In North Carolina, Harris' margins in Wake and Mecklenburg counties, home to the state capital of Raleigh and the state's largest city, Charlotte, respectively, will reveal how much Trump will need to squeeze out of the less-populated rural areas he has dominated.

In Pennsylvania, Harris needs heavy turnout in deep blue Philadelphia, but she's also looking to boost the Democrats' advantage in the arc of suburban counties to the north and west of the city. She has campaigned aggressively in Bucks, Chester, Delaware and Montgomery counties, where Biden improved on Clinton's 2016 winning margins. The Philadelphia metro area, including the four collar counties, accounts for 43% of Pennsylvania's vote.

Elsewhere in the Blue Wall, Trump needs to blunt Democratic growth in Michigan's key suburban counties outside of Detroit, especially Oakland County. He faces the same challenge in Wisconsin's Waukesha County outside of Milwaukee.

Where are the candidates?
Trump spent the very early hours of Election Day in Michigan, where he wrapped up a late-night rally in Grand Rapids. The Republican candidate plans to spend the day in Florida, where he is expected to vote in person -- despite previously saying he would vote early. He's scheduled to hold a campaign watch party in Palm Beach Tuesday night.

Harris plans to attend an Election Night party at Howard University in Washington, a historically Black university where she graduated with a degree in economics and political science in 1986 and was an active member of Alpha Kappa Alpha sorority. Aside from Howard, she has no public schedule announced for Election Day. Harris said Sunday that she had "just filled out" her mail-in ballot and it was "on its way to California."

Who's left to show up on Election Day?
It's unclear which voters will show up to cast ballots on Tuesday.

More than 82 million people voted early — either in person or through the mail. So many people already cast ballots that some officials say the polls in states like Georgia might be a "ghost town" on Election Day.

One major reason for the surge is that that Trump has generally encouraged his supporters to vote early this time, a reversal from 2020 when he called on Republicans to vote only in-person on Election Day. The early vote numbers confirm that millions of Republicans have heeded Trump's call in recent weeks.

The key question, however, is whether the surge of Republicans who voted early this time will ultimately cannibalize the number of Republicans who show up on Tuesday.

There are also shifts on the Democratic side. Four years ago, as the pandemic lingered, Democrats overwhelmingly cast their ballots early. But this time around, without the public health risk, it's likely that more Democrats will show up in person on Election Day.

That balance on both sides is critical as we try to understand the early returns. And it's on the campaigns to know which voters they still need to turn out on Tuesday. On that front, Democrats may have an advantage.

Trump's campaign and the Republican National Committee have outsourced much of their get-out-the-vote operation operation to outside groups, including one funded largely by billionaire Trump ally Elon Musk that's facing new questions about its practices. Harris' campaign, by contrast, is running a more traditional operation that features more than 2,500 paid staffers and 357 offices in battleground states alone.

Could there be unrest?
Trump has been aggressively promoting baseless claims in recent days questioning the integrity of the election. He falsely insists that he can lose only if Democrats cheat, even as polls show that show the race is a true toss-up.
Trump could again claim victory on election night regardless of the results, just as he did in 2020.

Such rhetoric can have serious consequences as the nation saw when Trump loyalists stormed the Capitol on Jan. 6, 2021 in one of the darkest days in modern American history. And unfortunately, there is still a potential of further violence this election season.

The Republican National Committee will have thousands of "election integrity" poll monitors in place on Tuesday searching for any signs of fraud, which critics fear could lead to harassment of voters or election workers. In some key voting places, officials have requested the presence of sheriff deputies in addition to bulletproof glass and panic buttons that connect poll managers to a local 911 dispatcher.

At the same time, Trump allies note that he has faced two assassination attempts in recent months that raise the possibility of further threats against him. And police in Washington and other cities are preparing for the possibility of serious Election Day unrest.

As always, it's worth noting that a broad coalition of top government and industry officials, many of them Republicans, found that the 2020 election was the "most secure" in American history."