President Donald Trump's decision to deploy US active duty troops and earlier deployment of National Guard forces to the southern border could cost between $200 million and $300 million, according to an independent analysis and Department of Defense figures on guard deployments.
The Pentagon has yet to determine the cost of the operation, nor has it identified the account where the funding would come from. But the Center for Strategic and Budgetary Assessments estimates that the cost of placing active duty troops on the border could range from $42 million to $110 million.
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That would be in addition to an estimated cost of $182 million for the already announced deployment of National Guard troops to the border in May.
CSBA says that on the high end, the deployment would cost $143 per troop per day for operating and maintenance costs and $112 per troop per day on the low end. CSBA also estimates that the use of military aircraft in this deployment would cost about $136,645 per day.
With the mission currently set to take place November 5 through December 15, for a total of 41 days, the cost of deploying 8,000 troops and air support ranges from approximately $42 million to $55 million, according to the CSBA estimate.
Trump has said the total number of troops could climb as high as 15,000, which CSBA calculates the price tag to be at approximately $90 million to $110 million.
When questioned on the cost of the operation on Monday morning Pentagon spokesman Col Rob Manning said, "I don't have a cost estimate for you, the Department will absorb the cost."
"Our Comptroller is working through that process right now, when we get to a point where we can provide a number we will certainly do that," he added.
Active duty US troops are barred from domestic law enforcement unless there is an emergency, but Trump has repeatedly raised the prospect of having troops enforce the border as he campaigns hard on the dangers of immigration ahead of the midterm elections.
Defense officials have repeatedly emphasized the troops at the border are there to support civil authorities and that they are not expected to come into any contact with migrants.
In April, Trump also directed the National Guard to support the Department of Homeland Security and Customs and Border Protection as they worked to secure the southwest border.
Some 2,100 National Guard troops are participating in that operation, which the Defense Department refers to at Operation Guardian Support.
In May, the Pentagon estimated that the cost of that assistance would be $182 million, which covered pay and allowances and per diem for 2,093 National Guard Personnel ($151M) and 12,000 flying hours for 26 UH-72 Lakota helicopters.
Both President George W. Bush and President Barack Obama deployed National Guard troops to help safeguard the southwestern border during their respective administrations.
Bush ordered Operation Jump Start, which lasted from 2006 to 2008, and deployed 6,000 National Guard troops to California, Arizona, New Mexico and Texas.
The cost of that operation was approximately $1.2 billion, according to a report by the Government Accountability Office.
In 2010, Obama ordered the deployment of up to 1,200 National Guard to the US-Mexico border as part of Operation Phalanx.
That operation cost $110 million in its first year. In 2012, the number of troops was scaled back as the focus shifted from boots on the ground to aerial surveillance.
National Guard deployments as part of named operations can carry greater costs when compared to active duty troops being sent as they can grant National Guard troops access to benefits that they would not normally receive.