What to watch for on Election Day when Harris and Trump face off

• The polling stations for the 2024 presidential election will close in a few hours.
• Kamala Harris and Donald Trump have battled for Pennsylvania, but each has multiple paths to victory.
• Here's what we're looking for.

Election Day 2024 has arrived. Billions of dollars have been spent to persuade voters to support particular candidates and causes.

Vice President Kamala Harris has turned the presidential race on its head with her late entry. Pre-election polls suggest the election could be the closest in history. Margins are so tight that a query error could result in unexpected data loss.

More than 78 million Americans voted early, either in person or by mail. Final turnout may be down slightly from the historic 2020 mark, but a Gallup poll found voter enthusiasm was above 2008 levels.

It's not just about control of the White House; it is also Congress. Republicans have a chance to retake the Senate as key elections took place on favorable terrain. The house is more difficult to project. Republicans could pick up a few seats, or Democrats could flip the chamber with an equally slim majority. New York and California, which are hardly competitive in the presidential race, play a large role.

Here's what we observe.

How Trump or Harris will win the White House

Harris' easiest path to victory remains what was once President Joe Biden's last resort: capturing the 2nd Congressional District of Pennsylvania, Michigan, Wisconsin and Nebraska – the so-called blue wall and blue dot. Barring any unexpected surprises, Harris would then win the Electoral College by 270 votes to 268.

Even the easiest path to former President Donald Trump's victory lies through Pennsylvania, the most important swing state. A win in Pennsylvania would likely allow Trump to retake the White House by holding North Carolina and unseating Georgia. In that scenario, he could even face the setback of losing votes in Nebraska, which pre-election polls show is very likely.

Although the focus is rightly on Pennsylvania, Trump spent a lot of time in North Carolina in the final days of the race, even though only two Democrats, Presidents Barack Obama and Jimmy Carter, have won the Tar Heel State since 1976.

Top counties to watch

Bucks County, Pennsylvania: Gov. Josh Shapiro recently called this Greater Philadelphia county “the swingest of swing counties in the swingest of swing states.” Hillary Clinton won the Bucks in 2016 by fewer than 3,000 votes and lost both the state and the White House. Biden won it four years ago by just over 17,000 votes, putting him on track to take the state by around 80,000 votes. If Trump wants to take back Pennsylvania, it's important to do well here.

Waukesha County, Wisconsin: Once traditional GOP turf, this Milwaukee suburb has changed along with other suburbs across the country. Trump beat Clinton here in 2016, but four years later his lead narrowed by just over seven points as he lost the state by about 21,000 votes.

Maricopa County, Arizona: In 2020, the home of Phoenix and one of the fastest-growing counties in the country flipped to Democrats by just over 2 points. Biden won the state by around 10,000 votes. Gov. Doug Ducey, a popular Republican, had won the district by nearly 14 points two years earlier.

What polls could tell us about early exit

Election surveys provide a first comprehensive overview of who voted. The embargo will be lifted at 5:00 p.m. ET, but concrete results indicating who might win in a state will be withheld until polls close in that area.

Although exit polls can provide valuable data, particularly on demographics, they are often misleading and uninformative.

Mark Blumenthal, a contractor at YouGov and previously director of polling at SurveyMonkey, told Business Insider he would be interested in how the vote breaks down by gender and race, particularly given speculation that Democrats are losing ground among blacks and Latinos voters.

Overall, however, he warns against placing too much emphasis on polls on election night.

“To see who will win between the time they are released, which is usually tomorrow at 5 p.m. Eastern time, and the time we get the final count, I advise them to ignore them,” said Blumenthal. “Ignore them completely. Go for a walk. Take a yoga class. Watch something on Netflix. Because they are not intended to tell us who the winner of the presidential election will be.”

Republicans are given priority over regaining control of the Senate

Michigan: Rep. Elissa Slotkin is trying to win a Senate seat that her fellow Democrats have held for 20 years. Former Rep. Mike Rogers, once a Trump critic, hopes the former president will overreach him. Rogers and his allies have focused on Slotkin's support for the White House's fuel efficiency standards, which do not require the production of electric vehicles but would likely lead the auto industry to produce more electric vehicles. Poll before the election: Slotkin rose about 3 points on the RealClearPolitics average.

Ohio: Sen. Sherrod Brown, a Democrat, has managed to weather challenges in the former swing state that now leans Republican. His challenger, Bernie Moreno, a Cleveland businessman, has pressured Brown over immigration. According to AdImpact, Ohio's Senate election is the most expensive non-presidential election ever. Poll before the election: Moreno was less than 1 point higher in the RealClearPolitics average.

Montana: Sen. Jon Tester, a Democrat, faces an even tougher challenge in Montana, a state where Trump leads by more than 16 points in 2020. Republicans worked hard to promote Tim Sheehy, a wealthy aerospace executive, despite failing to meet expectations of a painful primary. It doesn't happen. Like other Republican candidates, Sheehy has tried to link Harris to Tester. Poll before the election: Sheehy rose 6.5 points in the RealClearPolitics average.

The house is much closer

Arizona's 1st District: Republican David Schweikert has represented Scottsdale and its surrounding areas in Congress for nearly 14 years. Gov. Katie Hobbs and Sen. Mark Kelly handily won the area, one of the most educated districts still held by a Republican. His challenger, former Rep. Amish Shah, has highlighted his centrist record and hopes Trump's unpopularity will sink Schweikert.

New York's 19th: In 2022, Rep. Marc Molinaro was one of four New York Republicans to flip a seat held by a Democrat, which proved crucial to the GOP retaking the chamber. Democrats are hoping Josh Riley, a lawyer and political analyst, can win in a rematch with the help of Harris at the top of the ticket. More than $35 million was spent on the race, making it the most expensive House contest in the country.

California's 22nd: Rep. David Valadao is one of 18 House Republicans representing a district Biden won in 2020. Valadao is also one of the two remaining Republicans in the House of Representatives who voted to impeach Trump following the Capitol riot on January 6, 2021, like many Democrats in key races hoping to win in a rematch after losing two years ago had fallen short.