Chief Justice John Roberts Jr. on Tuesday said the word “shall” in immigration law means “shall.” But “what do we do,” he asked, if there are insufficient government resources to enforce the law’s command.

Roberts succinctly summed up the dilemma facing what appeared to be a divided court in the case United States v. Texas. The case stems from a lawsuit by Texas and Louisiana in which they successfully challenged immigration enforcement guidelines issued by the Department of Homeland Security last year.