(CNN) Results from the Washington state primary on Tuesday are another bad sign for Republicans.

We already know that Democrats lead in the House polls, and Republicans have a lot more seats at risk. Republicans therefore are hoping that the polling and the race ratings are overstating their vulnerability. They may be.

The outcome in Washington's primary however, suggest the opposite may be true. The polling and race ratings might be understating the Democrats' advantage. In other words, Democrats may actually be in slightly better shape than we think.

Washington, like California, uses a top-two primary system. That means all the Democrats and Republicans run in the same primary (with the top two vote-getters, regardless of party, advancing to the November general election).

Historically, the primary vote all the Democrats receive relative to all the Republicans is a good indicator of the fall result. As the New York Times' Nate Cohn pointed out in June, the top-two primary results are about as predictive as a poll taken within the final three weeks of the campaign. The catch, though, is that Democrats tend to do slightly better in the general election than in the primary.

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