Think of the numbers a Trump rally would have brought in! But this guy, Walker, was very ungrateful and asked him not to come. Sad!
If Walker loses (and if he does worse than in the general), it will be proof that it is because he did not have an in person in-state Trump rally. Rs will see that not supporting Trump and not using his help doesn't work.
If this was a normal Republican then that could be the interpretation, but Walker is one of the disastrous Trump candidates that wouldn't have been the nominee if not for Trump, much like Oz.
Though if Walker ends up winning, it could be seen as evidence that distancing from Trump is the right move.