This could be the closest presidential election since 1876

According to 538's latest election forecast, Vice President Kamala Harris has a 57-in-100 chance of winning the presidential election in November, while former President Donald Trump has a 42-in-100 chance. That means the race is essentially a toss-up; based on the closeness of the polls and the equivocacy of non-polling factors we call the "fundamentals," either candidate could easily win in November, and perhaps by a somewhat sizable margin if the polls significantly miss the mark (again).

Harris's advantage over Trump is slightly reduced from a couple of days ago. On Sunday, she had a 62-in-100 chance of winning the election, and we're now forecasting that she will win the national popular vote by 3.2 percentage points rather than by 4 points. The main reason for the decline is several good polls for Trump from The New York Times/Siena College published Monday morning. Those polls had Trump leading Harris by 2 points in North Carolina (our polling average is Trump+0.4), by 3 in Georgia (Trump+1.3 on average) and by 5 in Arizona (Trump+1 in 538's average). That last survey was a particular boon for Trump, given the pollster's last survey in Arizona had Harris up by 5 — a 10-point swing toward Trump.

However, our model is skeptical that Trump has made gains this large. That's because, while The New York Times/Siena College had good news for Trump, other pollsters have been releasing positive numbers for Harris — such as a Harris+5 national survey from NBC News released Sunday and a Harris+6 poll of Wisconsin released by MassINC Polling Group on Monday. Because our model sees support for Harris and Trump as correlated across states, it discounts when one pollster shows large movements that don't appear elsewhere. But don't just take our word for it; The New York Times's Nate Cohn suggested he is similarly skeptical, writing on Monday, "In circumstances like this, our rule of thumb is to toss the results into a polling average."

The bottom line right now is that the election remains incredibly close. Our model is currently forecasting that the margin between Trump and Harris will be less than 1 point in four states (North Carolina, Georgia, Arizona and Nevada), and within 4 points (the size of a normal polling error) in four more (Pennsylvania, Wisconsin, Michigan and Florida).

But the election isn't just close on the individual state level. It could also be historically close in the Electoral College. As the table above shows, there is currently a split between the northern battleground states, where Harris is currently leading, and most Sun Belt states, where Trump is currently leading. And this split makes especially tight Electoral College victories more likely.

For example, if you assume the forecast will be exactly correct and assign all states and congressional districts to the candidate who currently leads in them, and then you move Nevada just 0.8 percentage points toward Trump, Harris would win 270 electoral votes and Trump would win 268. That would be the smallest electoral-vote margin in a presidential election since 1876, when Republican Rutherford B. Hayes beat Democrat Samuel J. Tilden by one electoral vote. Even in 2000, Republican George W. Bush defeated Democrat Al Gore by the comparably comfortable margin of 271 to 267.

If those past elections are any guide, that could be a recipe for chaos in the weeks after Election Day. In 2000, the outcome of the election was murky for weeks as Florida, the decisive state that year, conducted multiple recounts. In 1876, the election result was disputed until just days before Inauguration Day, as some states sent conflicting sets of returns to Congress. In 2000, there were protests; in 1876, there were threats of violence. Here in 2024, it's possible that the losing candidate in such a tight race could contest the election in one or more states, which could in turn cause unrest among voters. Trump, for instance, has already called the veracity of mail-in ballots into question, and Republicans have begun suing state governments over registration processes they allege will let noncitizens vote in the election. And Trump has previously declined to rule out political violence from his supporters if he doesn't believe the election is fair.

But while the polls point to a close race today, the election is also "close" in the sense that small polling misses or slight changes in the national environment could lead to one candidate winning by a comfortable margin. The uncertainty about the outcome, in other words, makes things look "close" probabilistically (in the sense that each candidate has about an equal chance to win) but does not mean that big wins aren't also possible. According to our forecast, for example, there is a 1-in-6 chance that one of the candidates wins the popular vote by more than 10 points.

We'll be watching how Harris's and Trump's margins change in our forecast over the next few weeks in order to gauge the closeness of the race going into election night. Check back in on our polling averages and forecast as the race heads into its final six weeks!