President Donald Trump’s invocation of a wartime power to summarily deport Venezuelan nationals to El Salvador was “unlawful,” a federal judge ruled Thursday, blocking the administration from further deportations under the Alien Enemies Act of 1798.

Trump officials exceeded the scope of an 18th-century wartime law to deport some Venezuelan migrants, a federal judge in Texas said, halting its use.

The move exposed a quietly orchestrated deal between the president and El Salvador, culminating in a back-and-forth with a U.S. federal judge over the course of one frenetic day.