In this Oct. 27, 2018, photo, President Donald Trump speaks during a rally at Southern Illinois Airport in Murphysboro, Ill. Eager to focus voters on immigration in the lead-up to the midterm elections, Trump on Oct. 29 escalated his threats against a migrant caravan trudging slowly toward the U.S. border as the Pentagon prepared to deploy thousands of U.S. troops to support the border patrol. (AP Photo/Jeff Roberson)

WASHINGTON (AP) — The Pentagon said it’s sending 5,200 troops to the Southwest border in an extraordinary military operation ordered up just a week before midterm elections in which President Donald Trump has put a sharp focus on Central American migrants moving north in slow-moving caravans that are still hundreds of miles from the U.S.

The number of troops being deployed is more than double the 2,000 who are in Syria fighting the Islamic State group.

Trump, eager to keep voters focused on illegal immigration in the lead-up to the elections, stepped up his dire warnings about the caravans, tweeting, “This is an invasion of our Country and our Military is waiting for you!”

But any migrants who complete the long trek to the southern U.S. border already face major hurdles — both physical and bureaucratic — to being allowed into the United States.

In an interview Monday, Trump said the U.S. would build “tent cities” for asylum seekers.

“We’re going to put tents up all over the place,” told Fox News Channel’s Laura Ingraham.

“They’re going to be very nice and they’re going to wait and if they don’t get asylum, they get out.”

Under current protocol, migrants who clear an initial screening are often released until their cases are decided in immigration court, which can take several years.

Trump denied his focus on the caravan is intended to help Republicans in next week’s midterms, saying, “This has nothing to do with elections.”

The Pentagon’s “Operation Faithful Patriot” was described by the commander of U.S. Northern Command as an effort to help Customs and Border Protection “harden the southern border” by stiffening defenses at and near legal entry points. Advanced helicopters will allow border protection agents to swoop down on migrants trying to cross illegally, said Air Force Gen. Terrence O’Shaughnessy.

Troops planned to bring heavy concertina wiring to unspool across open spaces between ports.

“We will not allow a large group to enter the U.S. in an unlawful and unsafe manner,” said Kevin McAleenan, commissioner of Customs and Border Protection.

Eight hundred troops already are on their way to southern Texas, O’Shaughnessy said, and their numbers will top 5,200 by week’s end. Some of the troops will be armed. He said troops would focus first on Texas, followed by Arizona and then California.

The troops will join the more than 2,000 National Guardsmen that Trump has already deployed to the border.