So then Trump's voters would have voted for Bush or Rubio?
You are missing the point. There is only a small faction of the Republican base that is attracted to Ted Cruz. That is why he continually polls under 20% nationally.
If Trump were not in the race GOP voter turnout would be much lighter to start with since many people are only voting because of Trump. And a majority of GOP voters are just not as conservative or at least sounding conservative as Cruz. So yes they would have voted for one of the other candidates. Mitt I mean Scott Walker might have been able to be a contender if not for Trump. And I seriously retch as I say that. Rick Perry might have done better also.
Hahahaha! Exactly.