Cruz and McCain are already political foes. No one in the Senate apparatus likes Cruz or Mike Lee.
Cruz is a senator until he gets elected president. If he does not get the nod and McCain gets re-elected then it's back to status quo - McCain remain a scourge and Cruz is there to fight him.
He's not going to fight Donald's fight so he can score points with the McCain haters. He doesn't have to.....all of us that despise McCain (I am certainly one of them) would take the side of man like Cruz all day, every day even if Cruz never says out loud what we say to each other here.
“Cruz calls McCain an American Hero”
What a bunch of crap.