But that deployment could end up a very expensive one, and might not even be necessary.
"Members who are deployed in support of the Department of Homeland Security's border mission are not eligible for imminent-danger pay", he said in a statement Monday.
Manning said more than 7,000 active duty troops were expected to "soon" be supporting the Department of Homeland Security.
Trump did not rule out that the final number of soldiers deployed will reach 15,000.
At a White House speech on Thursday, the President suggested that troops should fire on migrants if they throw rocks, saying that rocks should be considered rifles and comparing the group of about 3,000 men, women and children to an "invasion".
According to the New York Post, "The soldiers worked with US Customs and Border Patrol officers to lay about 1,000 feet of fencing along the river, the Defense Department said". That doesn't mean shoot them. "But we're going to arrest those people quickly and for a long time", he told reporters. "Barbed wire used properly can be a attractive sight".
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And if you haven't already, go fucking vote. "And I say, all I'm doing is just telling the truth, what can I say?" he said. Trump quickly fired back at his White House predecessor, saying the former president didn't keep his promises to voters.
The initial DHS request was not accepted early on by the Pentagon and was not forwarded up the chain of command for approval. It's not clear if Mattis weighed in on the decision to reject the request for troops to perform law enforcement functions.
"Again, despite the noise in the media right now for all the reasons that we know, I would just tell you that the soldiers that are down there on the border right now know exactly what they are doing, they know why they are doing it, and they have the proper training and the proper equipment to do it", Dunford said.
It was unclear how many of those forces had taken up missions on the border, which will include support tasks like building housing for Customs and Border Protection personnel and erecting barriers. "But ... we don't anticipate that there will be that type of interaction" with migrants crossing the border illegally or seeking asylum.
The Posse Comitatus law forbids the USA military from enforcing domestic laws, unless there's no other choice.
These figures are in addition to the more than 2,000 National Guard troops that were deployed to the border in April.
Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford speaks during a press briefing August 28 at the Pentagon in Arlington, Virginia. Between 750 to 1,000 of those forces are Marines from Camp Pendleton.