Donald J. Trump is essentially two key states from the nomination.
By sweeping five states on Tuesday, he pulled only a few hundred Republican delegates short of the 1,237 he needs to win without a contested convention.
He has long been favored in the polls in two of the remaining primary states, New Jersey and West Virginia. That leaves Indiana and California as the crucial prizes that would put Mr. Trump over the top — and while he was once thought to be vulnerable in both states, polls have shown him with a modest lead.
Mr. Trump is by no means assured of holding his advantage, but it explains why his beleaguered rivals are now urgently coordinating to stop him in places where they believe they can beat him.
One big reason Mr. Trump’s math looks so good is something he has complained mightily about: party rules. In fact, the delegate rules (mostly favoring the winner, as opposed to proportional allocation) worked in his favor on Tuesday, and those rules allowed him to amass nearly half of the pledged delegates heading into the night, despite 38 percent support in the popular vote before Tuesday.
Mr. Trump won at least 105 of the 118 pledged delegates Tuesday, with the potential to win even more if the final count broke his way.
Mr. Trump even seemed likely to win unpledged delegates elected in Pennsylvania’s unusual “loophole” primary, the type of contest — focusing on gaining the loyalty of individual delegates — that has tripped him up so far this cycle. There, 17 delegates go to the statewide winner, but voters also directly elect 54 unpledged delegates to the Republican convention, and the Pennsylvania ballot includes no guidance on how these delegates might vote.
Mr. Trump’s preferred delegates led in 29 of the 54 slots. He may ultimately win fewer unpledged delegates than he would have if the state had adopted more typical rules, but he will not be shut out as he was in Colorado’s delegate convention.
Mr. Trump could be as few as 270 delegates from the 1,237 he needs when all of Tuesday’s delegates have been awarded.
He’s a safe bet in New Jersey and West Virginia, though he might not win as many delegates as he hopes in West Virginia’s delegate selection primary. He’s nonetheless likely to win at least 70 from those two contests, and perhaps as many as 85.
He could win a further 40 delegates (or even more) from three states that award delegates proportionally: Washington, Oregon and New Mexico. He is likely to garner a healthy share of delegates in those states, whether he wins or not.
He is an underdog in three winner-take-all states in the West and the Plains: Montana, South Dakota and Nebraska.
That leaves Indiana and California, the most competitive remaining contests and also the ones with the most delegates at stake. Neither state is thought to be as strong for Mr. Trump as the five states were on Tuesday, but Mr. Trump has led in every poll conducted in the two states since March. They have a combined 229 pledged delegates, and they’re awarded winner-take-all statewide and by congressional district.
If Mr. Trump wins both states, he will be favored to win the nomination. A clear win in California but a loss in Indiana would set up a contested convention where the unpledged Pennsylvania delegates could be decisive.
Mr. Trump’s opponents feel a particular urgency about defeating him in Indiana, which votes next Tuesday. Many believed that Ted Cruz was well positioned in the state after his clear win in Wisconsin, but three recent polls show Mr. Trump with a lead in the mid-single digits.
Mr. Trump’s position there explains the last-ditch effort of his rivals to coordinate their opposition. John Kasich, who is in third place in the state, agreed to withdraw ads, appearances and other resources from his Indiana campaign, effectively stepping aside. The idea, in theory, was to give Mr. Cruz a better chance of consolidating Mr. Trump’s opposition in the state. In exchange, Mr. Cruz would withdraw his campaign resources from New Mexico and Oregon — two proportional states where Mr. Trump’s delegate haul would largely be unaffected by the deal.
It’s hard to know whether the strategy will succeed. The pact has already shown signs of strain, with Mr. Kasich saying on Monday that voters in Indiana “ought to vote for me.”
What’s clear is that there isn’t much time for a Cruz comeback. His weak showing on Tuesday might make it even less clear to Republican voters that he is the principal anti-Trump option. The vote in Indiana is in just six days, and early voting is already underway.
If Mr. Trump wins Indiana, a merely modest win in California could be enough to give him 1,237 delegates.
Mr. Trump has led in all of the pre-election polls in California, sometimes by a double-digit margin, with around 40 percent of the vote. A modest victory could allow him to win over 100 of the state’s 172 pledged delegates, and perhaps far more.
In a way, the challenge in California by Mr. Kasich and Mr. Cruz is reminiscent of their challenge nationally. Mr. Trump has been thought to be beatable in California, but neither Mr. Kasich nor Mr. Cruz seems poised to build a coalition broad enough to defeat him.
Mr. Kasich is strong in the Bay Area and parts of Los Angeles; Mr. Cruz is stronger in parts of Southern California and the Central Valley.
The competing strengths of Mr. Trump’s opponents in California will make it harder for the two campaigns to coordinate than in Indiana. It’s unlikely that Mr. Kasich’s campaign will agree to withdraw its effort in the state, and with good reason: Mr. Kasich’s strength in liberal areas could help block Mr. Trump from winning congressional districts in Los Angeles and the Bay Area.
Instead, the two campaigns are reportedly considering a deal to divvy up which of California’s 53 congressional districts they will compete in. There is little precedent for this kind of alliance, and it’s hard to say whether it could be communicated well to voters who aren’t accustomed to sophisticated, district-by-district tactical voting.
There’s not much time for Mr. Kasich and Mr. Cruz to come to a decision. Ballots for the California primary will be mailed out in just two weeks, and nearly 80 percent of California voters cast ballots by mail.