The Defense Department plans to divert $3.8 billion from its military budget to pay for construction of a wall along the border with Mexico.
The Pentagon notified Congress on Thursday.
Congressional aides said the money was originally meant for the National Guard and for procuring big-ticket military hardware, such as F-35 fighter jets, C-130 transport aircraft, Osprey tilt-rotor planes, and shipbuilding.
Democratic lawmakers said the decision was dangerous and misguided.
The move also angered the top Republican on the U.S. House Armed Services Committee...
Representative Mac Thornberry of Texas said the Pentagon's plan was "contrary to Congress's constitutional authority."
The Trump administration has pledged to build at least 400 miles of wall along the Mexico border by November 2020, when Americans will vote for the next president.
As a candidate, Trump repeatedly promised that Mexico, not the U.S., would pay for the wall.