Because it was unsuccessful securing the amount of funding it wanted to build a wall on the U.S.-Mexico border, the Trump administration is moving ahead with its plan to deploy National Guard troops there instead.

The Pentagon has received a formal request from U.S. Customs and Border Protection (CBP) to provide support, which will require almost 2,100 of the 4,000 troops that Defense Secretary Jim Mattis initially authorized for the mission, according to two sources with knowledge of the request, including an official on Capitol Hill. The Defense Department estimates their deployment will cost $182 million, both sources said.

CBP has submitted a second request, which will likely require the remaining 1,900 Guard troops but the Defense Department is still reviewing it, one source said.

The Pentagon did not respond to a request for comment.

Both sources confirmed that none of the soldiers deployed will be doing wall construction and instead are providing support to CBP forces, which includes helicopter surveillance.

Trump has said the Guard troops will remain deployed to the border until the wall is built, but Mattis’ order only authorizes their deployment through Sept. 30.

The idea for the Guard deployment was hatched in March, when Trump became frustrated that Congress provided only $1.6 billion for the wall in its annual spending bill versus the $25 billion the Trump administration had been seeking. Trump, not understanding the restrictions on moving around funds already appropriated by Congress, turned to the Pentagon, suggesting its budget was big enough to be able to give some of its money away for construction of the wall. After considering other options, deploying the National Guard emerged as the least bad option for the Defense Department.

Mattis authorized the Guard deployment under Title 32 of U.S. Code, meaning it’s up to each state’s governor whether they want to send troops to the border. If they do, they will be reimbursed by funds from the Pentagon’s budget.

Arizona, New Mexico, Texas, Missouri and California have each agreed to send a few hundred troops, while other states, including Oregon, Montana and Nevada have so far said they wouldn’t deploy any Guard troops for this mission. The Democratic governors in those states have said they don’t believe the mission is being driven by security requirements, but instead stems from Trump’s political whims.

Trump is not the first to use Guard troops as political theater, both President Barack Obama and President George W. Bush authorized similar Guard deployments to the southern border to send the message that they were taking border security seriously.

Image: U.S. Army National Guardsmen scan the U.S.-Mexico border on June 22, 2011 in Nogales, Arizona. Photo by John Moore/Getty Images