Hillary Clinton has insisted that the Democratic primary contest against Senator Bernie Sanders of Vermont is behind her and that the party’s nomination is essentially hers.

Don’t tell that to Californians.

This week, Mrs. Clinton will begin her first full swing through the state to campaign before the June 7 primary.

After she delivers remarks at the Service Employees International Union’s convention in Detroit on Monday, Mrs. Clinton will head West for almost four days of fund-raisers and campaign events in Los Angeles, Orange County, Riverside, Salinas, San Jose and other parts.

Mrs. Clinton, a known and popular quantity who won California in 2008, has spent far less time in the state than Mr. Sanders. The Vermont senator and underdog has flooded California with rallies, commercials and organizers, hoping an upset win can help him convince superdelegates that he is the candidate best poised to defeat the presumptive Republican nominee Donald J. Trump in the fall.