Harvard Law School Professor Emeritus Alan Dershowitz called President Trump’s decision to declare a national emergency to fund the construction of a barrier along hundreds of miles of the U.S.-Mexico border a “mistake,” citing the expected onslaught of legal challenges.

“There will be a lawsuit. No doubt about it. It will be tied up in the courts for a long time. Ultimately, the Supreme Court will have to decide. And it’s unclear how the court will decide because it’s a new Supreme Court,” Dershowitz told John Catsimatidis on AM 970 in New York.