Cruz was down to Trump by as much as 8 points in the final polls before Iowa. Cruz won by 4.
How can a person not polling at the top of their own party beat Hillary - say, versus Trump
Yet Trump - who leads in his party's polls - consistently does the worst in national head to head polls against Hillary. Trump also consistently has the worst favorable's.
Rubio is currently 3rd in national polls. By your logic, since Rubio isn't at the top of his party's polls, he can't possibly win either.
Once again, Trump is known and is right where a Republican needs to be against Hillary. Cruz isn’t known, but when known he is dead.