No one had more fun with the news of the unusual alliance between Ted Cruz and John Kasich than the Republican front-runner himself, Donald Trump.

During rallies in Rhode Island and Pennsylvania Monday, the businessman used the term “collusion” to describe his rivals’ coordinated effort against him as conspiratorial and scheming. Colluding is illegal in business but allowed in the “rigged system” of politics, he told the crowd. "Actually I was happy, because it shows how weak they are, it shows how pathetic they are," he said.

Trump had a right to be gleeful – this partnership is far from perfect. The Cruz and Kasich campaigns had announced their alliance less than 24 hours earlier, and both candidates were already having trouble coordinating their message and working as a team. That said, the delegate math indicates the alliance may be the only way to keep Trump from securing the nomination.

The strategy so far involves Kasich backing out of Indiana’s winner-take-most primary on May 3 to pave the way for Cruz, and the Texas senator reciprocating in Oregon (May 17) and New Mexico (June 7), where delegates are awarded proportionally. With both candidates mathematically eliminated from clinching the nomination before the party’s July convention, each is staying in the race with the sole purpose of stopping Trump from becoming the standard-bearer.

The deal announced late Sunday night started to show cracks by Monday morning. Kasich declined to direct Indiana voters away from him and toward Cruz. "I've never told them not to vote for me – they ought to vote for me," he told reporters while campaigning in Pennsylvania, which hosts its primary on Tuesday. “But I'm not over there campaigning and spending resources; we have limited resources.”

Kasich scrapped an event in Indiana slated for Tuesday, but is still planning on attending a fundraiser in the state. Their campaign staffs struck the deal; the two candidates have not spoken directly to one another about the strategy and don’t have plans to do so. There is not a binding contract either, of course, so each candidate could step away at his convenience.

Both Kasich and Cruz tried to downplay the politics involved in the decision to form an alliance and were mindful of the appearance of telling voters what to do. “The voters in these states are very smart: they understand what the two campaigns are saying when you explain to them the resource allocation, and that the reason we came to this one-time agreement, which is to get to a convention,” Kasich chief strategist John Weaver told RCP. “The goal here is to ensure Donald Trump doesn’t get anywhere near 1,237.”

For his part, Cruz made it seem as though the plan came about more organically. “John Kasich has decided to pull out of Indiana, to give us a head-to-head contest with Donald Trump,” he said. “It’s good for the country to have a clear and direct choice.”

This development will add to the pressure facing the anti-Trump movement. Both Cruz and Kasich have called each other spoilers in their efforts to peel away delegates. If Kasich leaves Indiana, Cruz will be left without an excuse if he loses there.

The announcement of the alliance seems to suggest Cruz was concerned about his chances in the Hoosier State. Three polls last week found Trump leading the field by an average of six points. Cruz would easily close that gap if he won all of Kasich’s voters. But the math isn’t quite that simple. Some of Kasich’s voters might go to Trump and others might stay home. Also, some Kasich supporters might have already cast their ballots for him – early voting started on April 5.

But perhaps most importantly, if Kasich fails to coordinate effectively with Cruz (for example, if Kasich continues to tell Indiana constituents to vote for him despite saying he’s pulled out of the Indiana primary), it could confuse voters and make strategic voting more difficult. And while this alliance might be designed to more effectively marshal outside resources for both campaigns, the success of the partnership will ultimately hinge on whether enough voters coalesce around Cruz.

Despite all of the hurdles, the alliance is, from a delegate math perspective, probably the right course for anti-Trump forces. If this deal works and Cruz wins in Indiana, Cruz and Kasich will still be on track to keep Trump under the 1,237 bound delegates needed to guarantee nomination on the first ballot in Cleveland.

The math runs something like this: Trump will likely sweep Tuesday’s Northeastern primaries and net roughly 100 delegates. If he gets about two-thirds of the delegates in West Virginia (where the poorly designed ballots could keep his count down); roughly 45 percent of the delegates in proportional New Mexico, Oregon and Washington (which is a bit generous to Trump); and romps in winner-take-all New Jersey, he’ll have somewhere around 1,060 bound delegates.

It's easy to fiddle with this scenario and make it more or less favorable to Trump. But it demonstrates that Trump has three options to get to 1,237: upset Cruz in states where he’s favored, win both Indiana and California, or achieve an unlikely New York-scale delegate sweep in the Golden State. And if Cruz wins Indiana, where 57 delegates are at stake, he’ll knock Trump off track and force him to either attempt to win upsets in unfavorable upcoming states or try for very difficult margins in California.

Cruz would also get a solid delegate haul from winning Indiana – 30 delegates go to the statewide winner, and three go to the winner of each congressional district. Kasich arguably gets the worst end of this deal. Oregon and New Mexico award a total of 52 delegates, and both states are proportional. Kasich’s delegate share will closely track his vote share in Oregon (the same is true in New Mexico if all three candidates get over the 15 percent threshold). But if Cruz wins Indiana, those “winner-take-most” rules will likely give the Texan a disproportionate share of the state’s delegates.

If Cruz loses Indiana, it becomes much more difficult to stop Trump from getting to 1,237. If one adds 51 delegates from Indiana to the roughly 1,060 delegates cited above, it would put Trump somewhere around 1,110 delegates. If Trump were to win about two-thirds of the delegates in California, he would be within spitting distance of the 1,237 mark.

If Trump does win Indiana, it’s still possible to keep him from 1,237. But Cruz, Kasich and the anti-Trump forces would need to run an almost error-free campaign. Cruz would likely need to successfully defend all of the winner-take-all states where he’s favored (including Nebraska, Montana, South Dakota), while making sure Trump doesn’t win in California.

Indiana will likely then be the first – and potentially last – test for the Cruz-Kasich alliance and whether Trump can be stopped.

“We will know whether Donald Trump is the presumptive nominee on the evening of May 3rd or the morning of May 4th,” says Pete Seat, a Republican strategist in Indiana.

“We’re so close to the end that we should have as crystal clear of a picture as we can get in this election cycle of whether he is going to be the nominee on the first ballot.”

Caitlin Huey-Burns is a national political reporter for RealClearPolitics. She can be reached at chueyburns@realclearpolitics.com. Follow her on Twitter @CHueyBurnsRCP.