Ted Cruz stole the show Wednesday night at the Republican National Convention in Cleveland, when the Texas senator refused to endorse his party's nominee in his primetime speech and got booed off the convention stage because of it.
For Eric Trump, the eldest son of Donald Trump, the speech snubbing the nominee was a "classless" one.
Trump joined "CBS This Morning" Thursday, just hours after Cruz's impassioned speech to "vote your conscience" rather than vote with the party, and weighed in on the historic convention address.
"I think the people in this arena spoke for themselves," Trump said, referring to the raucous delegate dissent from the convention floor. "I thought it was classless, to tell you the truth. I thought it was a little bit classless."
"If you're going to a convention, you either support or don't go at all," he added.
Cruz's nearly half-hour long speech followed a nasty primary battle with the elder Trump, who regularly called Cruz "Lyin' Ted" on the campaign trail and repeatedly went after both Cruz's wife and his father.
"He signed a pledge at the beginning of this process," Eric Trump said. "When he didn't do the right thing people went crazy...This room, I've never seen boos like that, I never heard boos like that. The house, the whole auditorium was literally shaking with boos. I mean, how do you get booed out of your own convention? It was unbelievable."
In the wide-ranging interview, Trump also previewed his father's address on the final night of the convention.
"I think it's gonna be a deep speech, I think it's gonna be an important speech," he said. I think he's gonna talk about a lot of policy that he's talked about for the last 12 months and I think so much of the policy that quite frankly he's been right about over the last 12 months. "
"I think you're gonna hear probably the problems," Trump said. "But I think it's also gonna be a very optimistic speech in terms of how he as a commander in chief will be able to fix it."
Trump was asked about the GOP nominee's recent comments on how he would have to weigh, as president, whether he would honor the terms of a NATO alliance if Russia attacked Baltic state members.
Trump sought to clarify his father's remarks, saying "no, his message is actually, I think, a little bit different than that."
"He absolutely believes in NATO, he absolutely believes in living up to it," Trump said. But, "he wants people to pay their own way."
"I think his message is the fact that every country that's part of NATO should pay its own weight," he said. "Right now we subsidize the vast majority of NATO. How is that fair?"