The showdown over spending on immigration enforcement is the latest chapter in the mounting tension between the powers of Congress and executive branch.

Jordin Melgar-Salmeron was deported to El Salvador on May 7 despite an order from the U.S. Court of Appeals for the Second Circuit, New York, blocking it. The government has since denied that it violated the order, instead blaming the situation on a "confluence of administrative errors," according to a court filing last week.