A boy stands in the doorway of a polling station on June 5, 2018 in San Anselmo, California. California voters are heading to the polls to vote in the primary election.

Eight states held primary elections Tuesday, and returns indicate Democrats have a good shot of avoiding their worst fears in battleground California.

The results will play a major role in whether Republicans can defend their congressional majorities and stop Democrats from flipping the 23 seats needed to take the House. Just three of the states that held primaries on Tuesday — California, New Jersey and Iowa — will determine in large part whether Democrats in November can pick up the red seats they need to win a House majority.

California is one of the keys to Democrats' ambitions: The party is targeting as many as 10 Republican-held seats there. The state's primary system, which sends the top two candidates regardless of party to the general election, threatened to dash the party's hopes in some swing districts where several Democrats ran and split the vote.

While NBC News has not yet projected the two general election participants in the California swing districts, early results suggest Democrats could get a candidate into all of their targeted House general elections in the state.

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The most populous American state started the process of selecting a new governor, as well. Liberal Lt. Gov. Gavin Newsom won the gubernatorial primary, while John Cox, a businessman backed by President Donald Trump, will face off against him.