Once the Republican primary field was decided to be three candidates, it became apparent that Donald Trump was the only one who could get the 1,237 delegates needed for the nomination. So why would other candidates stay in? Essentially, because Donald Trump is an outsider candidate, those within the party were looking to try and stop him from getting to that delegate count. If he comes up short, then a contested convention can happen and the nominee can be changed.
So the goal for Cruz and Kasich was not to win the nomination, but rather to ensure Trump had a harder time getting there. In an effort to reach that goal, both candidates made a pact: Kasich would not campaign in Indiana, while Cruz would not campaign in Oregon and New Mexico. In theory, this would whittle the field down to two in each state making it more plausible to defeat Trump.
The Kasich campaign released a statement, saying, “Due to the fact that the Indiana primary is winner-take-all statewide and by congressional district, keeping Trump from winning a plurality in Indiana is critical to keeping him under 1,237 bound delegates before Cleveland. We are very comfortable with our delegate position in Indiana already, and given the current dynamics of the primary there, we will shift our campaign’s resources west and give the Cruz campaign a clear path in Indiana.”
At least on Cruz’s side, the plan did not work. He lost Indiana to Trump and ended his Presidential campaign the same day.