The active-duty troops are in addition to the 2,000 National Guardsmen that have been in place for the previous six months.
Trump says he's sending thousands of U.S. troops to stop an "invasion" of migrants at the U.S. -Mexico border even though the migrants are on foot hundreds of miles away.
Trump administration officials announced Monday that the additional troops would be deployed to join the estimated 2,100 National Guard troops that are already at the U.S. -Mexico border to assist with the approaching migrant caravan making its way from Honduras.
The forces are being dispatched to the border to deter two migrant caravans, each with several thousand migrants, headed to the USA through Mexico.
He describes the group on its Facebook page as helping protect the nation's borders. The Posse Comitatus Act of 1878 prohibits military personnel from conducting law enforcement functions on US soil, including physically detaining migrants.
O'Shaughnessy has also said that miles of barbed wire were sent to the border, and more Border Patrol personnel would also be delivered. "And sometimes enabling missions - especially if that's all you're going to do - require a significant footprint", he said, pointing out that USA troops deployed to the border will serve as "enablers" rather than "trigger-pullers".
In a separate incident on Sunday, migrants tore down a chain-link fence erected by Guatemalan authorities to block access to a bridge over the river at its border with Mexico, according to the Los Angeles Times. He claimed Mexican personnel were "hurt" and "unable, or unwilling to stop Caravan".
White House press secretary Sarah Huckabee Sanders on Wednesday praised Mexico for stopping the migrants from getting rides.
The leading caravan is still about 900 miles from the closest entry point into the US - but their intended route remains a mystery. On Wednesday, it said more than 7,000 troops would support the Department of Homeland Security along the border.
Trump ordered the latest troop deployment to the Southwest border earlier this week.
Thousands of Central American migrants resumed their slow trek through southern Mexico on Thursday, as immigration agents and police nibbled at the edges of the two caravans now in the country.
Adín Josué, left, and Juan Carlos, were deported from Mexico on October 30, 2018, after being found inside a migrant caravan. -Mexican border could go as high as 15,000 as he draws a hard line on immigration in the lead-up to the midterm elections. "Immigration is very important", Trump said.
Altogether, the four caravans represent just a few days' worth of the average flow of migrants to the United States in recent years.
Trump's administration plans to send about 5,200 U.S.
"We are waiting to see if they are going to help us out with buses, to continue the trip", said Lopez, 27. President Juan Orlando Hernandez was re-elected last November in an election many Hondurans suspected was fraudulent, but was recognized by the United States.