In not-breaking news, the 2024 race for the White House appears very close. Tellingly, 538’s latest presidential election forecast gives Vice President Kamala Harris the narrowest of advantages over former President Donald Trump — she wins in 57 in 100 simulations, making it practically a coin-flip race. To that point, the most critical swing states are all on a knife’s edge in the polls: Based on our latest state polling averages, Harris leads by around 1 to 2 points in Michigan, Nevada, Pennsylvania and Wisconsin, Trump holds roughly a 1-point edge in Arizona and Georgia, while North Carolina is essentially tied.
This group of battlegrounds is very likely to provide us with the eventual “tipping-point” state in the 2024 presidential election. If we line up each state (and the congressional districts in Maine and Nebraska) by how large the margin of victory is for the winner of that state — from most Democratic to most Republican, or vice versa — the tipping point is the contest that hands the Electoral College winner the clinching 270th electoral vote. That mark represents an outright majority of today’s 538 total electoral votes, which is necessary for someone to win the presidential election.
Of course, each presidential election has a tipping point, regardless of whether it’s a landslide, in which the tipping point is largely academic, or a nail-biter, in which we’re closely monitoring that state as a potential decider of the outcome — as could well be the case this year.
Looking at 538’s forecast, the most likely tipping-point state across all scenarios for the 2024 election is Pennsylvania. In 18 out of 100 cases, the Keystone State provides the winning electoral votes for either Harris or Trump.* The next-most likely tipping points are North Carolina, Michigan, Georgia and Florida, each of which have around a 1 in 10 shot of filling that role. Beyond them, the remaining scenarios mostly involve Wisconsin, Arizona, Texas, Nevada and Minnesota serving as the tipping point.
Even more notably, considering how close this election is, its outcome could rest entirely on which way the tipping-point state votes — making that state a “decisive” tipping point. As a result, the 2024 contest could join the short list of races absolutely decided by the outcome in that place — that is, contests in which neither candidate could win a majority in the Electoral College without capturing the tipping-point state.
Critically, Pennsylvania’s importance remains paramount in the smaller number of scenarios involving a decisive tipping-point state — which make up slightly more than 1 in 8 scenarios in 538’s presidential forecast. Now, thinking probabilistically, an event that has around a 1 in 8 chance of happening isn’t terribly likely to happen, but remains highly plausible. For instance, it’s about the same chance as flipping a coin three times and getting three heads in a row!
Among these more select cases, Pennsylvania has around a 17 in 100 shot of being the tipping point, followed by Michigan at about 14 in 100, North Carolina at 13 in 100 and Georgia at 11 in 100. The potential nail-biting involved in these scenarios could permanently damage your cuticles. Just consider that the vote count in Pennsylvania may be slow because election law prevents officials from beginning to process mail ballots before 7 a.m. on Election Day. And in Georgia, Republicans on the state election board have implemented rules to force cumbersome — and slower, more error-prone — hand counts of all votes at each precinct to check if the total matches the machine count, although those changes face a legal challenge to their implementation.
Regardless of the pace of the count, however, the campaigns and their allies well know how essential these states, especially Pennsylvania, are to winning in November. As of mid-September, Harris and pro-Harris groups had reserved about $76 million in ads in the Keystone State through Election Day, based on a recent analysis by AdImpact, compared with around $61 million by Trump and pro-Trump outfits. That combined total of nearly $137 million accounted for more than one-quarter of all ad bookings in the seven leading swing states, with (appropriately) Michigan the next-closest, with just shy of one-fifth (about $97 million combined). Pennsylvania has also hosted more presidential campaign events than any other state, per data from VoteHub, again followed by Michigan.
That Pennsylvania, Michigan or another key swing state could prove singularly decisive has positioned 2024 to potentially join a rare group of elections whose outcome rested solely on the tipping-point state. That’s been true of just seven of the 39 presidential elections from 1868 to 2020: four straight elections from 1876 through 1888, another in 1916 and two more in 2000 and 2004. The 2000 race effectively stands as the closest presidential election in history, as the decisive state (Florida) was decided by an absurdly small margin of 0.01 percentage points in favor of Republican George W. Bush.
The 2000 election was famously controversial for the balloting in Florida, which came down to just 537 votes out of a total of nearly 6 million cast there. That partly resulted from the ballot design used in populous Palm Beach County, which led some potential Democratic voters to mistakenly cast votes for third-party candidate Pat Buchanan instead of Al Gore. Four years later, Bush won in the Electoral College thanks to his 2-point edge in Ohio, which, had it flipped, would’ve given Democrat John Kerry a win in the Electoral College — perhaps while also losing the national popular vote, which Bush won by more than 2 points overall (no Democrat has ever won in the Electoral College while losing the popular vote). In line with these results, the polls in both Florida in 2000 and Ohio in 2004 were quite close in each state in the closing weeks.
We have to turn to the late 19th and early 20th centuries to find earlier presidential contests determined by a single state. Even more controversial than 2000, the 1876 election featured conflicting electoral vote submissions, rampant voter suppression of strongly Republican-leaning Black voters by white supremacist Democrats in the South and the strategic rejection of electoral returns by GOP election officials in three pivotal Southern states — including the tipping point of South Carolina, which was decided by 0.5 points. The 1880, 1884 and 1888 elections also stood on the razor’s edge, with New York serving as the tipping-point state in each at a time when it was the country’s most populous state. And in 1916, Democratic President Woodrow Wilson won reelection by the slimmest of margins by carrying California by 0.4 points.
Turning back to the 2024 race and the most likely state to decide it, the 538 forecast’s current median projection for Pennsylvania is about a 1-point victory for Harris. To be clear, that falls between the wide extremes of the forecast’s estimated range of outcomes in the state — a 15-point Democratic win to a 14-point Republican victory — so we shouldn’t be surprised if Harris or Trump wins the state by more than 1 point. But if a result in Pennsylvania played out close to that margin, there’s a real chance the Keystone State could join the ranks of decisive tipping-point states.
*Tipping-point state probabilities in this analysis were calculated based on the 538 forecast as of Sept. 26.