The new chairman of the House Armed Services Committee said that while President Trump could theoretically declare a national emergency to get a U.S.-Mexico border wall built, such a move would be a terrible use of federal money and be ripe for legal challenges.

“There is a provision in law that says the president can declare an emergency. It’s been done a number of times, but primarily it’s been done to build facilities in Afghanistan and Iraq,” Rep. Adam Smith, Washington Democrat, said Sunday on ABC’s “This Week.”

“In this case, I think the president would be wide open to a court challenge saying where is the emergency? You have to establish that in order to do this,” Mr. Smith said.