That is not quite fair, there are places Ted Cruz has polled over 50 percent of the republican voters.
Also I do think , assuming he wins the nomination that he will get the vast majority of republicans who liked trump, if faced with a Hillary alternative.
What I think he will not do is garner a lot of crossover votes. That is based on what I see locally in the Northeast, it may vary in other parts of the country.
Ted has been relatively weak in his adopted home state of Texas in Nov 2012 and this year’s primary. So I’d think it goes downhill from there in other less “red” states.