Except he didn’t use logic, he used false logic. Cruz is running against Trump, Rubio and Kasich, not just Trump. You might as well ask if he can beat Clinton why can’t Trump get 50% of the vote against such a scattered field? Same difference.
Perhaps you don't recognize using logic in the form of a question as using logic, but it most certainly is. Just a more subtle version of injecting logic into a conversation. It requires the person who answers to use logic to formulate their answer to the question. It required logic to formulate the questions where honest logical answers cannot be deployed. Not until the second place person can overtake the frontrunner. Until that point they are just wishful thinking.