Want to know November's election outcome? Washington's primary may be a crystal ball

The mantra “past performance is no guarantee of future results” applies to many things, including trying to predict election results ahead of time. But how many voters in a deep blue state showed up in this month’s primary - and how they voted - may provide insight into the political environment in November.

Election data analysts point to Washington state’s primary results as a useful barometer of which party is likely to win the national popular vote for the House of Representatives and to what degree.

Here's how to do it: add up the total votes for Democrats and Republicans in Washington’s 10 House district primaries. Then, take the difference between them and subtract 12 to get a rough estimate of the predicted House margin in November.

An NPR analysis of the Washington primary using this framework estimates that Democrats could win the national popular vote by about 4 points, which is slightly more than the 2020 presidential election that saw them narrowly win the White House and control of both chambers of Congress.

In other words, it will likely be yet another close race.

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