Voters in Alabama, California, Iowa, Mississippi, Montana, New Jersey, New Mexico and South Dakota headed to the polls Tuesday, the biggest flurry of activity yet in an already contentious primary season.

The Golden State is at the center of the action where competitive primaries and the state's "jungle primary" system have combined to create a uniquely challenging set of circumstances for both parties.

California's "top two" primary system where candidates of all parties compete against each other on one ballot has created the prospect of Democratic lockouts in key U.S. House seats up and down the state in districts they'll need to win in November if they want to make their dream of retaking the chamber a reality.