Trump made the remarks following a speech on Tuesday at the National Press Club in Washington, D.C., after being asked if he thought Christie was "too damaged" to be a viable candidate.
"Chris is a friend of mine, and he's a good guy," Trump said. "But he's got to get his problem cleared up. There's no question about it. You have to get that cleared up, and it has to come out very, very good."
Trump was referring to the George Washington Bridge lane closures, which caused a massive traffic jam in September in Fort Lee, N.J. The lane closures have since been tied to members of Christie's administration and to his allies at the Port Authority of New York and New Jersey. State lawmakers and federal prosecutors are investigating whether the closures were ordered as political retaliation. While lawyers hired by Christie's office have cleared the governor of any role in the plan to close the lanes, major questions still remain about how it originated and what motivated it.
"Obviously, it was foolish," Trump said Tuesday. "And I have spoken to him about it. It was a crazy set of events that took place. And I would say that Chris -- and I'll say it to anybody -- he has to get that whole thing straightened out and behind him, in which case he would be a viable candidate."
Still, Trump said, Christie has been "devastated" by the scandal.
"He's one email away from having a big problem," Trump said. "That has to disappear. It has to go away. And then certainly he'd be viable."