I know it means a lot to you Trump fans to think that old gasbag is some kind of John Wayne alpha male, but you're 100% wrong about Cruz's strategy.
He has said many times that negative attacks aren't his style. He prefers to stick to the Constitution and the issues. He campaigned the same way when he ran for the Senate.
It has nothing to do with Trump specifically.
Rubio and Cruz will be battling it out from now on. They both recognize that only one of them will survive to challenge Trump. I hope Cruz wins against Rubio. This will clear the field for a non-GOPe candidate.