"And I think the reason is what I was just saying, that if you look to the records of all the Republican candidates, there's a big difference between my record and that of everyone else if you ask, who has stood up to Washington?" Cruz told Cosby. "I think his involvement has been tremendously helpful to my campaign, because it's framed the central question of this primary."

But the question has always been to what lengths Cruz would go to avoid angering Trump, who has elbowed his rivals who threw the first blow. Cruz, who has made a reputation in Washington for battling his own party, has been the sole Republican not to do that.

Yet there has always been signs that the relationship was more short-term alliance than a long-term political friendship.

Cruz invited Trump to appear at an unusual two-candidate rally against the Iran deal largely, Cruz said, because of Trump's ability to get the media to cover it. And a top Cruz adviser once suggested that supporters of Trump at a rally were there to be "part of a show."

Trump, for his part, has said he would be open to hitting the Texas freshman should he climb too closely to Trump in the polls.