The military has shifted 160 troops on the southern border.
President Trump may not divert $89M intended for a military construction project to build his border wall, a judge ruled.
Navy leaders said they weren't consulted about billions being pulled out of military funds to pay for border barriers.
The plan to shift money has triggered rare Republican opposition to one of Trump's priorities.
Opposition is growing to the Defense Department's transfer of nearly $1.7 billion to fund the U.S.-Mexico border wall.
The acting Homeland Security secretary, Chad Wolf, is exercising authority under a 2005 law.
“Border security is national security,” Esper said, “and national security is our mission.”
Some of the programs targeted for reduction had been overfunded by Congress at levels above the military's original request.
Rep. Anthony Brown, D-Maryland, is the vice chairman of the committee and a retired colonel in the Army Reserve.
The fighting happened on once Mexican land that now constitutes the cities of Pico Rivera, Montebello and Whittier.