California Republicans filed a federal lawsuit to block Prop 50 maps, alleging racial bias and constitutional violations in redistricting.

Five incumbent Republicans must now choose between intraparty warfare or a run in districts designed for Democrats.

High-profile races are unfolding across the country on Tuesday, including New York City's mayoral election and governor's races in New Jersey and Virginia. In California, voters will consider a ballot measure that puts forth a redrawn congressional map that could net Democrats five House seats.

A University of California Berkeley/IGS Poll suggests 60% of likely California voters support Proposition 50, while 38% oppose it. The breakdown was highly partisan, with 93% of Democrats saying they would choose "yes" and 91% of Republicans choosing "no."