The Surprising Place Analysts Look to for Election Forecasting

Follow live updates on the 2024 election here.

Political polls, betting markets and statistical forecasts have become ubiquitous as November approaches. But there’s one predictive tool you may have missed: primary elections in Washington state, which took place last month.

It’s an indicator that election nerds pay particular attention to, for good reason: The general election results in the state a few months later tend to move in the same direction — whether becoming more Republican or more Democratic — as the rest of the country.

This year, results from Washington state are cause for some optimism among Democrats. They suggest a national environment somewhat similar to 2020, when Joe Biden outgained Donald J. Trump by 4.5 percentage points in the national popular vote and Democrats retained the House.

Here’s what to know about one of the lesser-known bellwethers of U.S. elections:

Why Washington?

Unlike the primaries of other states, Washington’s are strong predictors of its general elections. This is true for a few reasons.

• Washington has a top-two system in which all candidates, regardless of party, compete on the same ballot, with the top two advancing to the general election. This incentivizes candidates to campaign harder, to ensure they’re on the final ballot in November. And it motivates voters to participate rather than risk having their preferred candidate — or even their party — knocked off the ballot if they don’t vote.

• Voting is conducted almost completely by mail, and voters have almost three weeks to vote, which lowers the bar for participation. (Primaries that rely mostly or exclusively on in-person Election Day voting are more likely to attract only the most engaged sliver of the electorate.)

• The primary date is usually in August or September, much later than most other primaries, leaving less time for moods to change before the November election.

There are states with similar primary structures, and there are states with later primaries. But no state has Washington’s combination of primary structure, large voter numbers and late calendar date. Put them all together, and you get a high-turnout election with a broad, relatively diverse electorate just a few months before the rest of the country votes for president.

What does Washington’s primary tell us this year?

If you used only Washington’s primaries to forecast voting trends in the U.S. House, you’d do relatively well: The primary’s subtle shifts left or right have tracked with the country’s in all but two election cycles since 2000.

But Washington state and the country don’t just move in the same direction. They also tend to move one way or another by similar degrees. If after every Washington primary election between 2000 and 2022 you predicted that the country as a whole would shift left or right by the same level as the state’s primaries, you would have been off by less than three percentage points, on average. Pretty good!