WHITTIER, Calif. — For anyone wondering about the state of the Republican Party in California these days, consider this: There may be no Republican candidate for governor or United States senator on the state’s ballot this November.

That dispiriting possibility is beginning to sink in for California Republicans, against the backdrop of a divisive debate among its candidates and leaders on how the embattled party can become competitive again in a state where Ronald Reagan was elected twice as governor and that Richard M. Nixon called home.

It’s no secret the state’s Republican Party has been in a decline for 20 years. Its challenges have been aggravated by the election of President Trump, as he has pushed tougher policies on such issues as immigration and the environment, running up against strong and often bipartisan sentiment in California.

A field of Republican candidates for the United States Senate and governor is struggling against these headwinds as they seek to end a more than 10-year drought and elect a party member to statewide office. Under the California election system, candidates compete in an open, nonpartisan primary on June 5. The two candidates who get the most votes — regardless of party — advance to the November general election.