"Ted Cruz is a liar," he said. "I think he's a very unstable person. I have never had somebody take something you believe in and say the exact opposite."
Trump also criticized Cruz over mailers from his campaign in Iowa, which claimed some voters had a "voter violation."
"What he did to Ben Carson was a disgrace," Trump said. "That election in Iowa should be taken away from him."
"Had we had my immigration policies in effect, those people wouldn't have been in the country for the most part," Trump said. "I don't know if [Bush] lied or not. I know the CIA and other agencies knew something bad was going to happen. They did nothing about it."
Bush, who was on the campaign trail with his brother Jeb last night, stood by his leadership.
"Strength is not empty rhetoric. It is not bluster. It is not theatrics,” George W. Bush said. “This is a serious election for a serious job."