Washington (CNN) Ted Cruz said Thursday that he did not think Donald Trump would be the Republican nominee, his harshest criticism yet of a candidate he has assiduously avoided even brushing with judgment.

Asked by WABC Radio's Rita Cosby whether he believed that "eventually, you could beat him, based on your principles," Cruz said he could.

"I think that's right. I think that, in time, I don't believe Donald is going to be the nominee and I think, in time, the lion's share of his supporters end up with us," Cruz said in an interview taped Thursday that will air in full on Sunday.

Cruz, a generally cautious candidate and public speaker, has made no bones about courting the supporters of Trump, who has won over many fans of the conservative right. He has repeatedly needled his opponents for hitting Trump -- wisdom he again shared in the interview Thursday -- but Cruz has treated Trump as a serious, viable candidate.

And he has long maintained that Trump's rise would benefit the Cruz campaign, saying that Trump has encouraged voters to use a certain set of criteria to evaluate candidates that is favorable to Cruz.

"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.