President Donald Trump’s vision for a border wall along the southern U.S. border with Mexico took a big step forward Wednesday as a dozen companies from around the nation have been selected to compete on up to $5 billion worth of horizontal construction projects over a five-year period ending in 2024.

The awards come a year after requests for bids were first put out in response to Trump’s January 2017 executive order to secure the southern border, said Bobby Petty, a spokesman for the Army Corps of Engineers, which is overseeing the project on behalf of U.S. Customs and Border Protection. Though not specifically awarded to fund Trump’s February National Emergency Declaration that includes using up to $3.6 billion in military construction funds for a border wall, the corps could issue task orders under this program for that purpose, Petty told Military Times.

The projects will include a mix of border barrier, patrol and access roads, lights, access gates, drainage improvements, levee walls and other improvements, repairs and alterations along the border from California to Texas, Petty said.

Petty added that while the companies have been selected to bid on individual task orders for this project, the money to pay for them could come from either the Defense Department or CBP.

No individual tasks have yet been identified, Petty said, adding that they will be issued as needed until the $5 billion is spent or the 2024 deadline has expired.

A total of 38 companies originally put in requests for the project, a list that was winnowed down to a dozen and publicly announced Wednesday.

The barrier and the use of troops along the border have long been a political battle.

Democratic lawmakers want the head of the Pentagon to drop plans for military personnel to directly interact with migrants on the U.S. southern border, arguing it could violate America’s long-standing separation of the military and law enforcement.

In the latest flashpoint in the military’s growing role at the border, 19 Democratic senators, including several presidential hopefuls, sent a letter to acting Defense Secretary Patrick Shanahan on Wednesday urging him to revoke waivers he granted to nearly 280 of the more than 4,000 troops on the border. They also want a legal justification for “military protective activities” that Trump has authorized troops to perform.

“We urge you to revoke these waivers to prevent the continued escalation of military involvement in immigration enforcement activities and the further politicization of the use of servicemembers to inappropriately respond to a divisive domestic policy issue,” reads the letter, led by Sen. Richard Blumenthal, D-Conn., and a senior member of the Armed Services and Judiciary committees. The letter was obtained by Defense News.

Last week, Shanahan approved a plan to send 320 more active-duty troops to the U.S. border with Mexico in response to another support request from Customs and Border Protection.

About 3,200 active-duty service members are currently deployed for those missions, which began last October. In addition, several thousand more National Guard troops have been working in similar support roles since April 2018.

Also last week, White House officials announced plans to send a $4.5 billion emergency supplemental budget request to Congress for “humanitarian needs,” that includes building more processing facilities and buying more food for immigrants arriving at the southern border.

Of that total, about $377 million will cover the costs of military deployments. None of the money will be used for wall construction, a senior White House official said.

Congressional Democrats have accused Trump of militarizing the immigration debate by unnecessarily deploying active-duty troops to southern states. Troops there have been conducting various support roles like barrier placements, but have had limited contact with migrants seeking entry into America.

The current authorities for the military missions runs through September. But Shanahan told lawmakers that Homeland Security’s personnel shortfalls could total “thousands” of people, casting doubt when the military could be replaced by civilian staff.

“We’re now in the position to ask how long will we be there,” he said. “We’ve gone through, looked at the conditions at the border … We need to get that into a sustained environment.”