The U.S. Department of Justice on Wednesday made good on its threat to sue Texas over a new state law that would let police to arrest people suspected of crossing the border illegally. The suit, filed in Austin federal court, argues that Senate Bill 4 — approved last year by the Republican-controlled legislature — impinges on the federal government’s authority to regulate immigration and manage international borders. The Justice Department is asking the court to reject Texas’ law as unconstitutional.