Or - Scott Walker dared to endorse someone besides Trump, so Trump will find a reason to criticize him. And, he criticized Walker for not raising taxes, but Trumpsters will ignore the actual substance - if it were a Democrat doing the same thing, that Democrat would be excoriated.
News flash! Trump knew all along that Walker would not endorse him. Now that Walker has officially endorsed Cruz it is in Trumps best interest to minimize the endorsement. Thats what Trump is doing. Its called politics!