Donald Trump is riding high on a wave of momentum after a series of commanding victories in contests the political world knew would be good for the front-runner, but which nevertheless buffeted his message of inevitability at a crucial time in the contest.

With the critical, more evenly matched contests of Indiana and California ahead in the final stretch of the primary season, Trump will need to carry that momentum through to the end. If Cruz and the #StopTrump movement can break the Trump wave in Indiana and evenly contest California, the party will be all but set for a contested convention, and an uncertain outcome for the front-runner. If not, the race will be all but over.

All the states with contests remaining send only bound delegates to the convention. With the exception of West Virginia, where delegates are directly elected by name, the eight other primaries will be shaping the first ballot landscape of the convention at the polls.

Each of the states matter on the margins — but the fate for Trump and the GOP will be truly settled in Indiana and California. The reason has everything to do with the arithmetic and process.

[lz_table title=”Remaining GOP Delegates Up for Grabs” note=”Based on Trump delegate count as of 4-26″]Date,State,Delegates
May 3,Indiana,57
May 10,Nebraska,36
May 10,West Virginia,34
May 17,Oregon,28
May 24,Washington,44
June 7,California,172
June 7,Montana,27
June 7,New Jersey,51
June 7,New Mexico,24
June 7,South Dakota,29
|Total Remaining,502
|Total Trump Needs,287
[/lz_table]

Montana, South Dakota, and New Jersey are pure winner-take-all contests, accounting for 107 of the remaining 502 delegates up for grabs. But the trio is largely spoken for. Trump is heavily favored to take New Jersey and Cruz has handily won states surrounding Montana and South Dakota.

Nebraska awards nine of its 36 delegates to the winner of each of its congressional districts and the remainder to the statewide victor. Here again Cruz is heavily favored, having won every bordering state save for South Dakota, which hasn’t yet voted.

West Virginia is a unique animal in the zoo of arcane process and procedure that governs the distribution and selection of delegates late in the usually settled GOP contest. The state directly elects its delegates, bound to the candidate of their choice. Trump is largely expected to be strong in West Virginia, but is unlikely to sweep the state because of Cruz’s ability to recruit delegate candidates with their own name recognition and appeal.

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But even if Trump should somehow run the track on country roads, and other expectations hold, the front-runner would remain 202 short of the magic 1,237 number to secure a first ballot win.

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Oregon, Washington, and New Mexico apportion their delegates proportionally according to the results to each candidate who meets a minimum threshold of support: 3.57 percent in Oregon, 15 percent in New Mexico, and 20 percent in Washington.

In a newly formed and unprecedented political alliance, Cruz has vowed not to contest Oregon and New Mexico and will encourage his supporters to support Kasich in those two proportional states.

In Washington, a new survey shows the field tightly clustered in the low single and double digits, with most of the electorate remaining undecided. The survey released by the Elway Poll on April 21 showed just 11 percent apiece for Trump and Cruz and 6 percent for Kasich.

If Trump receives anywhere from 20 to 70 percent of the proportional delegates from these three states he will be approximately 135 to 183 delegates short of 1,237 (Trump has so far won roughly 40 percent of proportionally apportioned delegates). That will be roughly the number Trump needs to win in Indiana and California in order to stave off a contested convention.

Indiana will be first and the most critical to determining whether Trump will command the momentum of the race in the final push.

[lz_table title=”Most Recent Indiana GOP Poll” source=”CBS News/YouGov”]Candidate,Support
Trump,40%
Cruz, 35%
Kasich, 20%
[/lz_table]

Indiana will shell out 57 delegates on May 3 — and 27 of them are bound three apiece to the winner of each of the state’s nine congressional districts. The remaining 30 delegates are all awarded to the statewide winner. Polls show Trump with a slight lead in the state over second place Cruz, but no poll has been conducted since the Cruz-Kasich alliance was announced and Kasich began encouraging his supporters to back Cruz.

Kasich has a significant body of support in the state bordering Ohio. The most recent poll from CBS News/YouGov shows Kasich pulling 20 percent of the field to Trump’s 40 percent and Cruz’s 35. If the numbers in Indiana remain static and Kasich retains 5 percent of his current 20, then Cruz would need to win roughly 2 out of every 3 of Kasich’s other supporters in order to pull ahead of Trump. Should Cruz scoop up more than 2 of every 3 Kasich voters, he could comfortably beat the front-runner.

Sen. Marco Rubio pulled a similar kamikaze move to boost Kasich in the Ohio GOP primary, but at the time polls showed Rubio with only 5 percent support in the Buckeye State. Kasich’s attempt to move his supporters en masse to Cruz is a much more ambitious and novel team strategy. It will not be the only factor in determining the crucial outcome in Indiana but could certainly be the difference maker.

That leaves California and its massive 172 delegate take. No matter the outcome in previous contests Trump will likely come to the final day of voting short of 1,237. What matters will be how short and how many delegates he can win in California. Trump will arrive on the final day of primary voting with a set number he needs to hit in California. What remains to be seen is whether that number is easy, doable, or highly unlikely for the front-runner to prevent a contested convention showdown.