Candidates are making a final push for votes ahead of a primary election in which Republicans could propel two women to the top of their party's ticket for the first time.
Billionaire former eBay chief executive Meg Whitman and former Hewlett-Packard CEO Carly Fiorina were campaigning in Southern California on Monday.
Republicans hope the anti-incumbent mood that has swept the nation will help them defeat two of California's most well-known Democrats: state Attorney General Jerry Brown, who is seeking a comeback as governor, and U.S. Sen. Barbara Boxer, who is running for a fourth term.
Brown and Boxer have been raising money in anticipation of difficult general election campaigns. A union-funded group that supports Brown reports raising more than $4 million in the last two weeks.