Cruz repeatedly told Beck there are only two choices for president this November: Trump or Hillary Clinton, the Democratic nominee.
"What I said is this is a binary choice," he said. "I wish it were not a binary choice. As you know, I tried very very hard, as did you, to prevent it from being a binary choice between Hillary and Donald Trump."
"I am still encouraged by you to abandon my principles and vote because it's a binary choice?" Beck quipped back.
"You are encouraged by me to do what you believe is right and honorable and principled," Cruz said.
Beck pressed the former 2016 presidential hopeful, asking him what changed between the "vote your conscience" speech he delivered at the GOP convention in Cleveland and now.
"This is information that you had in Cleveland. ... You had all this information. You had this information the day you dropped out of the race and said that Donald Trump is a 'sociopathic liar.' So you had all this information," Beck said.
He continued: "Have you spent an enormous amount of time — do you have new information that has made you say, 'Oh my gosh. He's now not a sociopathic liar? He's not the guy that I very eloquently spelled out for over a year. And now suddenly there's a reason to believe him?'
"You knew all the things you are saying today," Beck reiterated. "The time to do that would have been the day you pulled out, or the day you gave the speech so eloquently. Why now? What's new?"
Cruz said that "the most significant thing that changed" was the Supreme Court list Trump released on Friday, which added Utah Sen. Mike Lee, a Tea Party favorite.
"I think to me critically committed the only nominees he would consider for the court were on that list," he said. "Now that was a major shift."
Beck, running short on time, bumped a commercial break to ask Cruz if a Politico report that said he rented his email list out to Trump months before endorsing was accurate.
"Did you sell your list to Donald Trump?" Beck asked.
"Well Glenn, as you noted, you sell advertising. That's what actually funds your radio show and that's true, as far as I know, of every radio show. That's how one communicates," Cruz said.
The senator continued: "That's also true of every candidate. You don't sell your list, but you rent your list, so if someone wants to access your supporters, they pay for it. And that helps fund your effort. And like every other candidate, sure, we have rented our list out to those who wish to pay for it."
Cruz then took a swipe at Politico, calling the story Beck referenced a "hit piece" from a "left-wing rag."
Following the marathon grilling session, Beck said he was wrong about the man he thought Cruz was.
"For the for the very first time I heard Ted Cruz calculate," Beck said of his interview with Cruz. "And when that happened, the whole thing fell apart for me. And it's my fault. It's my fault for believing men can actually be George Washington. It's my fault."