Donald Trump escalated his attack against Ted Cruz on Wednesday while the Texas senator sought to move past the hits and maintain his status as the favorite to win the Iowa caucuses.

In separate interviews with CNN, Trump and Cruz squared off over the businessman’s comments — reported Tuesday in The Washington Post — that the senator’s birth in Canada could pose a “big problem.” Trump told CNN’s Wolf Blitzer that Cruz, whose mother was a U.S. citizen, should go to court and ask a judge to rule that he’s eligible to run for president.

“How do you run against the Democrat, whoever it may be, and you have this hanging over your head if they bring a lawsuit?” Trump said in an interview that aired on “The Situation Room.”

Trump said Cruz should to ask a judge for a “declaratory judgment” that Trump said would protect Cruz against any future questions about his eligibility that could come in a general election.