Donald Trump Says He's 'Very Seriously' Considering Suing Ted Cruz Donald Trump talked with ABC News' George Stephanopoulos on "GMA" today.

 -- Republican presidential front-runner Donald Trump says he is "very seriously" considering suing GOP rival Sen. Ted Cruz.

"I’m thinking about it very seriously," Trump told ABC News' George Stephanopoulos on "Good Morning America" today. "I’ve never dealt with anybody who lies like him."

Trump pointed to his own positions on gun rights, as well as the dismantling of President Obama's signature health care law, saying that the Texas senator was misleading voters about his stances.

"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."

Trump also continued his criticism of former President George W. Bush for his handling of the 9/11 terrorist attacks.

"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."