A single tipping point could come in the 2024 election

In non-breaking news, the race for the White House in 2024 appears to be very close. Significantly, 538's latest presidential election forecast gives Vice President Kamala Harris the slimmest advantage over former President Donald Trump – winning in 57 out of 100 simulations, effectively making it a coin toss race. Until then, the most critical swing states in the polls are all on a knife edge: Based on our latest state polling averages, Harris is ahead by about 1-2 points in Michigan, Nevada, Pennsylvania and Wisconsin, with Trump leading by about 1-2 points . Arizona and Georgia are ahead in points, while North Carolina is essentially tied.

This group of battlegrounds will most likely give us the final “tipping point” in the 2024 presidential election. If we base each state (and the congressional districts in Maine and Nebraska) on how large the margin of victory is for that state's winner – from most Democrats to most Republicans or vice versa – the tipping point is the contest that the Electoral College won the decisive 270th electoral vote. This mark represents the absolute majority of the total 538 electoral votes required for someone to win the presidential election.

Of course, there is a tipping point in every presidential election, whether it is a landslide, where the tipping point is largely academic, or a tailspin, where we watch that state closely as a potential decider of the outcome – like it could well be the case this year.

Looking at the 538 forecast, Pennsylvania is the most likely tipping point state for the 2024 election under all scenarios. In 18 cases out of 100, the Keystone State will deliver the winning votes for either Harris or Trump.* The next most likely tipping points are North Carolina, Michigan, Georgia, and Florida, where there are about 1 in 10 votes each to fill that role. In addition, the remaining scenarios primarily refer to Wisconsin, Arizona, Texas, Nevada and Minnesota as tipping points.

Even more strikingly, given how close this election is, its outcome could depend entirely on which way the tipping point state votes – which could make that state a “pivotal” tipping point. As a result, the 2024 contest could enter the short list of races decided solely by the outcome there — that is, contests in which neither candidate could win an Electoral College majority without reaching the tipping point.

Crucially, Pennsylvania's importance remains paramount in the smaller number of scenarios with a key tipping point state – accounting for just over one in eight scenarios in the 538 presidential forecast. If you think probabilistically, the probability of an event occurring with a probability of occurrence of around 1 in 8 is not very likely, but remains highly plausible. For example, the chance is about the same as flipping a coin three times and getting heads three times in a row!

Among these more select cases, the probability of Pennsylvania being the tipping point is about 17 out of 100, followed by Michigan at about 14 out of 100, North Carolina at 13 out of 100 and Georgia at 11 out of 100. The potential thrills associated with these scenarios could permanently damage your cuticles. Just keep in mind that vote counting may be slow in Pennsylvania because election law prohibits officials from starting processing mail-in ballots before 7 a.m. on Election Day. And in Georgia, Republicans on the state election board have introduced rules to force a cumbersome — and slower, more error-prone — manual count of all votes in each county to verify that the total matches the machine count, although those changes are legally challengeable too their implementation.

Regardless of the pace of the count, however, campaigners and their allies know exactly how important these states, especially Pennsylvania, are to winning in November. By Election Day through mid-September, Harris and pro-Harris groups had set aside about $76 million for ads in the Keystone State, compared to about $61 million for Trump and pro-Trump groups, according to a recent analysis by AdImpact. That total of nearly $137 million accounted for more than a quarter of all line items in the top seven swing states, with (appropriately) Michigan being the closest at just under a fifth (about $97 million combined). Pennsylvania also hosted more presidential campaign events than any other state, followed by Michigan, according to data from VoteHub.

That Pennsylvania, Michigan or another key swing state could prove particularly decisive has positioned 2024 to potentially join a rare group of elections whose outcome depends entirely on the tipping point state. That was true in only seven of the 39 presidential elections from 1868 to 2020: four consecutive elections from 1876 to 1888, another in 1916, and two more in 2000 and 2004. The 2000 race is effectively considered the closest presidential election in the History The crucial state (Florida) was decided in favor of Republican George W. Bush by an absurdly small margin of 0.01 percentage points.

The 2000 election was notoriously contentious, with only 537 votes cast in Florida out of a total of nearly 6 million votes cast. This was due in part to ballot design in populous Palm Beach County, which caused some potential Democratic voters to mistakenly vote for third-party candidate Pat Buchanan rather than Al Gore. Four years later, Bush won the Electoral College thanks to his two-point lead in Ohio, which, if flipped, would have given Democrat John Kerry an Electoral College victory – but perhaps also the loss of the national popular vote suffered by Bush won overall by more than two points (no Democrat has ever won the Electoral College and lost the popular vote at the same time). Consistent with these results, polls in both Florida in 2000 and Ohio in 2004 have been fairly close in recent weeks in both states.

We must turn to the late 19th and early 20th centuries to find previous presidential elections decided by a single state. The 1876 election was even more controversial than 2000, marked by conflicting votes, rampant voter suppression of heavily Republican-leaning black voters by white supremacist Democrats in the South, and the strategic rejection of votes by Republican election officials in three key Southern states – including the tipping point by South Carolina, which was decided by 0.5 points. The elections of 1880, 1884 and 1888 were also on a knife edge, with New York being the turning point in each case at a time when it was the most populous state in the country. And in 1916, Democratic President Woodrow Wilson won re-election by a narrow margin, carrying California by 0.4 points.

Back to the 2024 race and the most likely state that will decide it: The current median 538 forecast for Pennsylvania is for a 1-point win for Harris. To be clear, this falls between the extremes of the forecast's estimated outcome range for the state – a 15-point Democratic win and a 14-point Republican win – so we shouldn't be surprised if Harris or Trump winning the state by a margin of 15 points more than 1 point. But if the result in Pennsylvania is anything like that, there is a real chance that the Keystone State will join the ranks of crucial tipping points.

footnote

*The turning point probabilities in this analysis were calculated based on the 538 forecast dated September 26th.