In 2020, polls overestimated Joe Biden’s margin over then-President Donald Trump in competitive states by about 4 percentage points. The margin between Harris and Trump in the final polling averages of 538 for the 2024 race is 2 points or less — less than half the 2020 error — in seven states: the familiar septet of Arizona, from Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin. This means that, if the 2020 polling error repeats itself, Trump would win all seven swing states and 312 Electoral College votes.
Of course, if the polls are wrong, it won’t necessarily benefit Trump. It is impossible to predict in advance the direction of the polls’ error, and polls have overestimated Republicans many times in the past. In a scenario where polls overestimate Trump’s margin by 4 points in every state, Harris would win all seven key states and 319 electoral votes.
Both of these outcomes – and everything in between – are very much on the agenda today. But are these scenarios really probable, or rather external possibilities? Well, that’s where the work we do for our election forecasting model can help. According to our latest presidential forecasts, Trump and Harris have almost identical chances of winning the White House.
Based on the magnitude of polling errors in the past, our election model estimates that the average polling error in competitive states this year will be a 3.8 point margin. In other words, the model expects a polling error of about the magnitude of 2020 – but not necessarily in the same direction as in 2020. (In 50% of the model’s simulations, Trump beats his polls , and 50% of the time Harris does it )
Because the seven key states are so close, even small polling errors in the same direction can have a big impact on who wins the election. According to our model’s simulations, there’s a 60/100 chance that either candidate will win more than 300 Electoral College votes — something Harris could do by winning five of seven swing states and Trump six of seven. By modern standards, I think it’s fair to consider this a resounding victory – given how closely divided the country is, it’s relatively unlikely that either candidate would win much more than that . (Even to get 320 electoral votes, Trump would have to win a state like Minnesota and Harris would have to win a state like Florida.)
Of course, the likelihood of an explosion one way or the other depends heavily on the outcome of the popular vote. This is clearly visible in the graph below, which takes all the simulations of our model and groups them by popular vote result:
As you can see, Trump is favored to win the election even if he loses the popular vote by 1-2 points, which is what our national polling average currently suggests. And if the national polls prove to be underreported, and Trump wins the popular vote by 1 to 2 points, he would be favored to achieve a resounding victory.
Meanwhile, our model estimates that Harris needs to win the popular vote by 2.1 points to be favored and win the election, because swing states lean more Republican than the nation as a whole. And if she wins the popular vote by 4.5 points (Biden’s 2020 popular vote margin), she is favored to win in her own victory.
