The troops deployed to the southern U.S. border to support existing border authorities once a band of Honduran migrants completes its journey from southern Mexico will cost $220 million, CNBC reported, citing two anonymous sources.

There are about 4,000 troops near the border since this weekend and, ultimately a total of 15,000 could be deployed if Trump gets his way. According to documents detailed by Newsweek and the Washington Post, the military itself expects only “a small percentage of the migrants will likely reach the border.” A risk assessment by the Defense Department “found that the caravan did not pose a threat to the United States,” and that “the caravan would take about a month and a half to get to the U.S. border,” according to CNBC.

So far troops at the border have been seen laying down barbed wire. Active duty servicemembers can’t act as law enforcement officers in the United States, leaving the troops at the border to support the authorities already there.

About 4,000 migrants are in Veracruz, according to the Associated Press, and are heading for Mexico City next. Other groups of migrants are making their way north from the Mexican states of Oaxaca and Chiapas farther to the south. Mexican authorities said there were “more than 5,000 migrants in total currently moving through southern Mexico via caravans or in smaller groups,” according to the AP. Almost 3,000 migrants have “pursued refugee status” in Mexico since the caravans starting entering the country last month.

This hasn’t stopped President Trump from exploiting the caravan—and the supposed threat of migration from Mexico and Central American more generally—as one of his central pitches to voters ahead of the midterm elections Tuesday. In a speech from the White House on Thursday, which some expected to announce an overhaul to asylum policy, Trump instead gave his typical campaign speech about immigration.

The Trump campaign bought airtime on Sunday Night Football for an ad featuring a Mexican who killed two California sheriff’s deputies while being illegally present in the U.S. Trump had previously tweeted a version of the ad, which falsely blamed Democrats for letting the man into the country, and CNN had refused to run it because it was racist. NBC announced Monday morning that the ad was “insensitive” and that the network would “cease airing it across our properties as soon as possible.”