SAN FRANCISCO — President Donald Trump is moving fast to spend billions of dollars to build a wall on the Mexican border with money secured under his declaration of a national emergency, but he first must get past the courts.

On Friday, a federal judge in Oakland, California, will consider arguments in two cases that seek to block the White House from spending Defense and Treasury Department money for wall construction. California and 19 other states brought one lawsuit; the Sierra Club and Southern Border Communities Coalition, represented by the American Civil Liberties Union, brought the other.

On Thursday, a federal judge in the nation’s capital will consider a bid by the U.S. House of Representatives to prevent Trump from spending any Defense Department money for a border wall.

At stake is billions of dollars that would allow Trump to make major progress on a signature campaign promise heading into his campaign for a second term.

The president’s adversaries say the emergency declaration was an illegal attempt to ignore Congress, which authorized far less wall spending than Trump wanted. Trump grudgingly accepted congressional approval of $1.375 billion to end a 35-day government shutdown on Feb. 15 but declared an emergency in almost the same breath. The White House says it has identified up to $8.1 billion that it could spend.

Trump’s actions “amount to a usurpation of Congress’ legislative powers in violation of bedrock separation of powers principles embedded in the Constitution,” the state attorneys general wrote.

The administration argues that the president is protecting national security interests as unprecedented numbers of Central American asylum-seeking families arrive at the U.S. border with Mexico.

“The increasing surge of migrants, the highest in over a decade, has placed a tremendous strain on the limited resources of the Department of Homeland Security and exacerbated the risks to border security, public safety, and the safety of the migrants themselves,” the Justice Department said in a court filing.

Defense Department Transferred $1 Billion to Border Wall

The courtroom showdowns come amid a flurry of activity to accelerate wall construction. Kenneth Rapuano, an assistant secretary of defense, said in a court filing last month that work on the highest-priority, Pentagon-funded projects — in Yuma, Arizona, and in New Mexico — could begin as soon as May 25.

The Defense Department transferred $1 billion to border wall coffers in March and another $1.5 billion last week. Patrick Shanahan, the acting defense secretary, may decide as soon as Wednesday whether to transfer an additional $3.6 billion.

Last month, the Army Corps of Engineers awarded a $789 million contract to SLSCO Ltd. of Galveston, Texas, to replace 46 miles of barrier in New Mexico, paid for by Pentagon funds.

On Wednesday, Barnard Construction Co. of Bozeman, Montana, won a $141.8 million contract to replace 5 miles in Yuma and 15 miles in the Border Patrol’s El Centro, California, sector. Southwest Valley Constructors of Albuquerque, New Mexico, won a $646 million contract to replace 63 miles in the Border Patrol’s Tucson, Arizona, sector. All of those projects are funded by the Defense Department, with construction expected to begin in as little as 45 days.

Also this week, the Department of Homeland Security waived environmental impact and other reviews to replace a wall in California and Arizona under a law that gives the secretary sweeping powers to spec construction.

The environmental waivers cover a 15-mile replacement in El Centro that is funded by the Homeland Security Department’s 2018 appropriations and was awarded in a contract to SLSCO last year. The administration said construction could begin on that project as early as Saturday.

Aside from California, states participating in the legal challenge are Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Massachusetts, Michigan, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont, Virginia and Wisconsin.