This year, Democrats won about 57.3% of the Congressional primary vote to Republicans’ 41.3%, or a margin of 16%. Subtract 12 percentage points, and you get that estimate of a 4% popular vote victory for Democrats later this year.

Current presidential polling averages have Vice President Harris leading former President Donald Trump by about 3% heading into the Democratic National Convention, and the most recent NPR/PBS News/Marist poll also found Harris up by 3%, suggesting a similar national environment could be waiting in November.

In recent elections, the framework has also hinted at the direction of public sentiment ahead of the general elections, like the 2022 midterms. Democrats finished with a 10.4% margin in Washington’s primary election, a down year that suggested Republicans were favored by about 1.6%, closer to the final national popular vote advantage of about 2.8% for the GOP in the House.

In 2020, a 14% primary margin suggested a 2% popular vote victory for Democrats, which ended up being closer to 3%. 2018’s “blue wave” that saw Democrats win the House popular vote with a roughly 8.5% margin was foreshadowed by Washington’s primary that saw a 20.4 % Democratic margin across its Congressional seats.