In setting a June 7 primary, the California Legislature last year had all but conceded that voters in the nation’s most populous state once again would be no more than an afterthought in the presidential primaries.

This might be the rare moment in the past four decades when the California primary looms large in at least one, and perhaps two, of the major-party nominations.

The big variable is what happens in other primaries, starting Tuesday.

“If (John) Kasich and (Marco) Rubio can win their home states (Ohio and Florida, respectively), then the (contested) convention strategy is in full play and (Donald) Trump will be showing vulnerability,” said Rob Stutzman, a prominent California GOP strategist who has embraced the stop-Trump strategy. “If Trump wins both, or even one of those states, then I think we’re into a (Ted) Cruz vs. Trump race and I think it could absolutely come down to California.”

Less likely, but still possible, is Sen. Bernie Sanders remaining competitive against Hillary Clinton in the Democratic primary when Californians vote.

California is always caught in a difficult predicament. If it moves its primary to an early date — such as it did in 2008, when Clinton’s Feb. 5 victory here helped keep her campaign afloat against Barack Obama — it must maintain a second primary in June for congressional and state legislative primaries. Otherwise, nonincumbent candidates for those mostly local offices must basically put their lives on hold for two years to run for election.

Yet that split-primary option comes with a high cost: nearly $100 million in 2008 when all state and county costs are calculated.

The prospect of a June primary with the Republican or Democratic primaries in doubt offers some intriguing side effects.

Back to Gallery California primary may yet count 2 1 of 2 Photo: Alan Diaz, AP 2 of 2 Photo: Joe Raedle, Getty Images



An intense and undecided Republican primary could compel that party’s voters to the polls and thus elevate the chances that one of its U.S. Senate candidates, Tom Del Beccaro or Duf Sundheim, will make it to a runoff against Democratic state Attorney General Kamala Harris or U.S. Rep. Loretta Sanchez.

An aside: California’s “top two” primary system — in which the top two finishers appear in the general election regardless of party — does not apply to the presidential primary. Only registered Republicans and Democrats will receive ballots for each party’s presidential race.

Which brings up another possible variable: Voters have until May 23 to register for the primary.

“Maybe some will register against Trump,” Stutzman observed. “A great irony would be if Latinos actually register Republican to vote against him. I think GOP voters in California would react to Trump like GOP voters most anywhere else, which means about 1 in 3 want to vote for him, and two-thirds don’t.”

A brief history lesson:

California initiated its presidential primary in 1912, when Teddy Roosevelt defeated President William Taft — as was the case in eight other states — but lost the nomination at the Chicago convention.

Throughout the 20th century, primaries remained a relatively secondary element of the nomination process nationwide. Tony Quinn, a pre-eminent authority on California trends and demographics, noted that in 1968 Sen. Robert Kennedy did not announce his candidacy until March 16 — and won only three before California. President Lyndon Johnson dropped out of the race on March 31.

“Thus you had a two-month sprint to California, which played a vital role that year and probably would have assured Kennedy’s nomination had he not been killed the night of the primary,” Quinn said.

Vice President Hubert Humphrey, the favorite of party bosses and eventual 1968 Democratic nominee, entered the campaign too late to enter any primaries.

Quinn maintained that the biggest barrier to California clout is not the late date, but its change from winner-take-all primaries to the awarding of delegates based on the result in each of the 53 congressional districts. Especially with the divide between the more liberal coastal areas and more conservative inland districts, it’s difficult for any presidential candidate to emerge with a bounty of delegates.

“Campaigns understand that California really is not worth the expenditure of millions of dollars because you really don’t win that much,” Quinn said.

The old winner-take-all system helped Republican Sen. Barry Goldwater (1964) and Democratic Sen. George McGovern (1972) secure a huge haul of delegates to assure their nominations. It didn’t prevent either from losing a landslide election in the fall, but that’s another story.

The refreshing upshot is that the competitiveness of this year’s primary races increases the chances that presidential candidates soon will be coming to the Golden State for reasons other than raising campaign contributions.

John Diaz is The San Francisco Chronicle’s editorial page editor. Email: jdiaz@sfchronicle.com Twitter: @JohnDiazChron

The big statewide showdown: the race to succeed Democratic Sen. Barbara Boxer

California will have an open U.S. Senate seat for the first time since Boxer and Sen. Dianne Feinstein were victorious in 1992, often referred to as “The Year of the Woman” in American politics.

The four contenders to succeed her have agreed to an April 25 debate to be conducted by journalists from The San Francisco Chronicle and KCRA-TV at the University of the Pacific’s main campus in Stockton. The 90-minute debate is scheduled to begin at 6 p.m. It will be video-streamed online on the Chronicle and KCRA websites, and the broadcast will be made available to stations in each of the state’s media markets. The Bay Area station has yet to be determined.