I wouldn’t take this attack to mean that Cruz has gained mainstream credibility. But it is an attack to paint him as an extremist. This will be his major challenge in this campaign regardless of how we view him here. The big question is not how he plays in Texas but can he generalize that conservative appeal to the rest of the country.
But why bother? No one is really attacking Rick Santorum, Mike Huckabee, Rick Perry, Mike Pence or even Jeb Bush.