The best way to defeat Donald Trump is that the 3 candidates who are still in the race battling the Trump work together instead of fighting themselves. By denying a win to the Donald for as long as possible they will hurt the Trumpster enough to change the projector y of the race. Here’s a sketch of how it work (below)?
(1) Kasich & Rubio would say that they are not actively seeking votes in the Michigan Primary.
(2) In return Rubio & Cruz would agree to back away from the Ohio race.
(3) Finally Cruz & Kasich would pull out their resources in Florida.
(4) The three candidates would continue on this path until one of them doesn’t win the state that they expect to be most competitive in then that said candidate would pull out of the race.
By completing these simple steps it would make it more likely that there would either be a brokered convention or one of the three would emerge as the dominant candidate.