Ted Cruz and John Kasich are teaming up in an effort to stop Donald Trump’s quest to reach the 1,237 delegates needed to win the Republican nomination. In Cruz and Kasich’s partnership, Kasich agreed to stop campaigning and running ads in Indiana and Cruz agreed to back off in Oregon and New Mexico.

This deal is centered on helping Cruz in Indiana, which is a winner take all state at both the state level and congressional district level. Preventing a Trump win in Indiana is a crucial step in the #NeverTrump movement and Kasich ceding the state to Cruz should give him enough votes to win, assuming Kasich’s voters decide to vote for Cruz, which is not a given. New Mexico and Oregon are proportional, and with neither Cruz nor Kasich capable of winning enough delegates before the convention to win the nomination, who wins those states isn’t all that important.

Obviously only one of these candidates can be the Republican nominee so the Cruz-Kasich partnership will be short lived, but it has the potential to be effective. If the voters vote tactically as Cruz and Kasich clearly want them to do, Indiana can be a crucial step in stopping Trump from winning the nomination. On the flip side, if Trump wins Indiana despite Cruz and Kasich colluding to stop him, the narrative will likely shift in Trump’s favor and many will feel that his victory is inevitable. Right now, Indiana is the most important primary in deciding whether Trump will win outright, or if the Republican Party will be headed for a contested convention.