Flags fly outside of the U.S. Customs and Border Protection building in El Paso. (Sarah L. Voisin/The Washington Post)

The Pentagon announced Monday night that it has authorized the transfer of up to $1 billion to the Army Corps of Engineers to build additional barriers along the U.S.-Mexico border, a move that drew sharp objections from Democratic lawmakers.

The shift in funds, which the Pentagon justified under President Trump’s declaration of a national emergency at the southern border, will facilitate the construction of 57 miles of “pedestrian fencing,” road construction and lighting along stretches of the border in Arizona and Texas.

The money, according to top Pentagon officials, was shifted from the Army after recruiters failed to hit targets that would have required the funds.

Ten senators, including Patrick J. Leahy (Vt.), the top Democrat on the Appropriations Committee, objected to the move, saying in a letter that the Pentagon had not sought approval of congressional defense committees.

“As a result, we have serious concerns that the Department has allowed political interference and pet projects to come ahead of many near-term, critical readiness issues facing our military,” said the letter to acting secretary of defense Patrick M. Shanahan and Secretary of Homeland Security Kirstjen Nielsen. “The $1 billion reprogramming that the Department is implementing without congressional approval constitutes a dollar-for-dollar theft from other readiness needs of our Armed Forces.”

Although the clash highlighted ongoing tensions between the Trump administration and Democrats in Congress, the move was in keeping with what the administration has pledged to try to make good on Trump’s marquee promise of a border wall.

Earlier this month, Trump vetoed a measure passed by both the House and Senate to nullify his declaration of a national emergency at the border. Trump is using the measure to spend more on border barrier funding than Congress has authorized.

The Democrat-led House voted Tuesday to override Trump’s veto, but the effort fell short. The finally tally was 248-181, short of the 288 that would have been necessary.

The $1 billion outlay announced Monday night would help “block drug-smuggling corridors across international boundaries of the United States in support of counter-narcotic activities of Federal law enforcement agencies,” the Pentagon said.

It’s part of a total of $2.5 billion that the administration plans to take from the Pentagon budget for the wall this year using a counterdrug law that allows the defense secretary to build fences, lighting and roads for other federal agencies in designated drug corridors. The president doesn’t need to invoke a national emergency to use that authority.

Because the counterdrug account at the Pentagon contains little money, the Defense Department is finding funds elsewhere in its budget that can be moved into the account through a process called “reprogramming” to comprise the $2.5 billion. Traditionally, the Pentagon receives sign-off from Congress when it moves significant amounts of money in its budget, though approval isn’t required by law. This time, the Pentagon isn’t asking for sign-off, because lawmakers would reject its request.

The result is a break with a long-standing tradition that Rep. Adam Smith (D-Wash.), chairman of the House Armed Services Committee, pressed Shanahan on during a congressional hearing Tuesday. Smith said that by disregarding the long-standing “gentlemen’s agreement,” the Pentagon would probably lose its authority to reprogram funds from the appropriations committee in the future.

“What was the discussion like in deciding to break that rule, and what is your view of the implications for it going forward in terms of the relationship between the Pentagon and Congress in general?” Smith asked the acting defense secretary. “And specifically how much is it going to hamper you to not have reprogramming authority after this year?”

Shanahan admitted that by moving the money for the wall without agreement from Congress, the Pentagon is risking losing its leeway to move around money longer term. He acknowledged that’s a downside that will “hamper” the Pentagon in the future, and suggested that the White House overruled the Defense Department on the matter.

“It was a very difficult discussion. And we understand the significant downsides of losing what amounts to a privilege,” Shanahan said. “The conversation took place prior to the declaration of a national emergency. It was part of the consulting that went on. We said, ‘Here are the risks longer term to the department,’ and those risks were weighed, and then given a legal order from the commander in chief, we are executing on that order.”

In addition to the $2.5 billion for the wall Trump intends to take from the counterdrug account, he plans to take an additional $3.6 billion from the military construction budget using a law that requires the invocation of emergency powers. Known as Section 2808 of the U.S. code that governs the military, that law allows the defense secretary, in the event of a national emergency requiring the deployment of the armed forces, to take military construction money for projects in support of those troops.

Gen. Joseph F. Dunford Jr., Chairman of the Joint Chiefs of Staff, said his office is analyzing the projects the Department of Homeland Security has asked the Pentagon to complete under that law to decide whether they would in fact support forces deployed to the southwest border. Shanahan will then issue a determination on that matter once the analysis is complete.

Shanahan is widely expected to agree that the projects support the troops so as to follow the letter of the law and allow Trump to take military construction funding for the wall.

Meanwhile, questions emerged at a Senate Arms Services Committee hearing Tuesday about the $1 billion the Pentagon said it would be moving from Army personnel funds into the counterdrug-account to fund the wall.

Sen. Jack Reed (R.I.), the top Democrat on the committee and a former Army officer, said the Army has a $2.3 billion unfunded priority list for fiscal 2020 that comprises projects for which the service does not have money.

Army Secretary Mark T. Esper responded that the money has been reprogrammed from the Army’s military personnel account after it could not find enough soldiers to meet its planned number of recruits.

“In a sense, you are forgoing at least the immediate use of those funds for military purposes like aviation readiness, is that correct?” Reed asked.

“The needs always exceed the means, so yes, we could have used that money as the other services to continue to approve our readiness,” Esper said.

Reed said the Army also has identified more than $500 million in unfunded infrastructure projects, and asked how detrimental it would be to readiness if they are not completed.

“Senator, we need to see what projects will be teed up for repurposing, and I think that once we see those initial requests, we can better see what the impact will be,” Esper said.

In the same hearing, Sen. Gary Peters (D-Mich.) pressed Esper and Army Gen. Mark Milley, who has been selected to be Trump’s next chairman of the Joint Chiefs of Staff, saying it appears that the administration is pulling an “end-around” by reprogramming money from the Army to the Pentagon’s counterdrug fund, which in turn will be used to fund the wall.

“How is the southern border a greater priority for the Army than readiness and modernization?” he asked.

Esper said that the Army met its goals for readiness and modernization in the 2019 budget, and said he “doesn’t see it the way that you have characterized it, if you will.” But he agreed under questioning that the money also could have been reprogrammed to meet shortfalls elsewhere in the Army.

“But you’re saying that the southern border is more important than readiness,” Peters pressed.

“I’m not saying that,” Esper said. “I’m saying that the Department of Defense made decisions based on what the president set as priorities, and we are following through. We are executing.”

Milley said that maintaining a ready Army is the service’s top priority and modernizing is its second, but he cited the need for civilian control of the government.

“It is not for me to say one is important than the other relative to the whole national security of the United States,” Milley said. “Within the Army, we have said that priority one is readiness and priority two is modernization. But within the nation, that is not our call.”

Erica Werner and Felicia Sonmez contributed to this report.