The DOJ’s opinion is just that. It is an opinion. It is not law. It is not precedent. It is an opinion that has to be argued before a court. The DOJ also said that torture was a great idea. The duty of the DOJ is to provide cover for whatever the President wants to do.
Or they will try to throw out the D.C Attorney Generals suit for lack of standing since D.C. is the federal seat, not a state.