Barring another big shift in the race, such as a decision by one of the three remaining candidates to drop out, the contest for California will be critical to the outcome. How important is it?
So important that Kasich gave the state — home to one of every eight Americans — a shout-out in his nationally televised victory speech Tuesday night.
"I'm getting ready to rent a covered wagon, we're going to have a big sail and have the wind blow us to the Rocky Mountains and over the mountains to California," Kasich told cheering supporters outside of Cleveland.
California's 172 delegates — 14% of the 1,237 required to win the nomination — will be chosen on the last big day of the presidential calendar, which also features voting by New Jersey and a smattering of other states.
California has moved up its primary day in past cycles in order to boost its importance, but now appears ready to seize that role on its traditional voting day: the first Tuesday after the first Monday in June.
After Tuesday night, "California's primary delegates became the pot at the end of the rainbow for the campaigns," said Ben Ginsberg, a veteran GOP lawyer who has long been involved in the nomination process.
The party now looking at an outsized role has been losing heft in California for years. The most recent registration numbers show 4.76 million Republicans registered in the state, or 27.6% of registered voters. That represents a loss of nearly a million voters from the party's registration peak in 2004.
The Republicans who will decide this year are more similar to their counterparts in other states than they are to California as a whole. Republicans in this majority-minority state are 76% white, 62% married and 33% over the age of 65, according to a September USC Dornsife/Los Angeles Times poll. In all those areas, those numbers greatly exceed the percentages among registered voters.
The USC/Los Angeles Times survey, conducted less than three months after Trump entered the race, had him in the lead, with 24% compared with the next finisher at the time, retired neurosurgeon Ben Carson, at 18%. The other two candidates who now remain in the race, Texas Sen.
A more recent poll, a January survey by California's Field Poll, found a very different race: Among likely Republican voters, Cruz had 25% to Trump's 23%, a statistical tie, with Kasich nearly invisible.
The Field Poll results suggested that California's campaign will rest on the same dynamic that has defined much of the GOP battle across the country this year: whether voters are attracted to Trump's take-no-prisoners economic appeal, or are put off by the controversies that have surrounded his campaign as a result of his comments on women, Mexicans, other Republican candidates and violence toward protesters at his rallies.
The way Republican delegates are awarded in California creates the potential for a tactically complicated campaign. The vast majority of delegates are awarded, three at a time, to the winner of each of the state's 53 congressional districts.
A GOP candidate could get three delegates by winning House Minority Leader
That could mean 53 separate fights, in theory, although in practice much of the warring will be conducted via the state's dozen or so media markets.
Cruz has pursued the strategy of targeting Republicans in overwhelmingly Democratic districts, most recently in Missouri. Cruz, who launched his effort here last summer, is by far the best organized candidate when it comes to California.
"Most other Republican presidential campaigns' strategy for California sounds like a burger chain — In-N-Out. They fly in, raise money and get out," said Ron Nehring, a former state party chairman who is Cruz's California chairman turned national spokesman. "Our philosophy has been completely different."
Trump recently signed on strategist Ted Costa, who launched the successful 2003 recall of Democratic Gov. Gray Davis. Costa declined to discuss Trump's strategy, but said the businessman-turned-reality-television star would find favor with the state's voters.
Kasich has won California endorsements — notably former Gov. Arnold Schwarzenegger — but his campaign has no organization here. And Schwarzenegger left office unpopular with many Republicans, which could undercut the impact of his endorsement.
More helpful to Kasich would be financial support among the moderate Republicans who helped finance Schwarzenegger's two successful statewide campaigns.
At this point, the California scenario for 2016 looks remarkably similar to what occurred in 1964, when the state handed Republican Barry Goldwater a victory, giving him momentum heading into the national convention. Although he lacked the full number of delegates needed for the nomination, he won it anyway, before his landslide defeat by Democratic President
To avoid a contested convention in July, Trump would have to capture more than half of the delegates who remain in play.
"We always hope, cycle after cycle, maybe this is the year we're the jewel at the end of the contest," said GOP strategist Reed Galen. "Donald Trump again appears to have won Tuesday night but not put away his opponents. If he can't finish them off soon, California may finally have its day in the sun."
The Democratic battle this year between
Because of the party's nominating rules — the proportional allotment of delegates coupled with Clinton's edge with so-called superdelegates who are not bound by voting results — Sanders would have to amass big wins in several large states to have a hope of catching up.
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