The cost of deploying troops to the US-Mexico border to help deal with three incoming caravans of Central American may cost as much as $220 million, according to CNBC, citing two US defense officials who were not authorized to speak publicly.

The estimate, which could change on the ultimate size and scope of the mission, comes amid the deployment of approximately 4,000 troops to the border on Saturday ahead of the first caravan's arrival - which has dropped in size from an initial 7,000 to under 4,000 as participants have either accepted asylum in Mexico or turned around.

Trump has made the caravan one of his prime targets as he campaigns for Republicans down the stretch of the midterm election campaign. The president has referred to the caravan as an "invasion" while claiming that Democrats want open borders. Critics have called the deployment a political stunt. Defense Secretary James Mattis, however, downplayed that criticism last week. "The support that we provide to the secretary for homeland security is practical support based on the request from the commissioner of customs and border police. We don't do stunts in this department," he said Wednesday. -CNBC

CNBC also wants you to know that the caravan does not pose an immediate threat to the United States, according to a Pentagon risk assessment reported by "a person with direct knowledge of US intelligence," who we assume isn't a fan of stopping the incoming migrants. The person added that the caravan would take around a month to reach the US border, which we assume means on foot.

On Sunday we reported that newly arrived US troops had placed around 1,000 feet of razor wire fencing along the Texas side of the Rio Grande river underneath the McAllen-Hidalgo International Bridge, as three separate caravans of Central Americans make their way north in the hopes of claiming asylum.

Soldiers participating in "Operation Faithful Patriot" are working with US Customs and Border Patrol officers to install the fencing, according to the Department of Defense.

U.S. Army troops, part of “Operation Faithful Patriot” arrived to the U.S. border with Mexico, deployed by President Trump ahead of midterms. Soldiers spread out barbed wire along the Rio Grande in south Texas. #immigration #border #caravanamigrante #undocumented #army pic.twitter.com/PVD6YIbCvk — John Moore (@jbmoorephoto) November 2, 2018

The Department of Defense estimates that over 7,000 troops will be stationed in Texas, Arizona and California, while a second caravan of around 1,000 - 1,500 people trails the first - crossing from Central America into Mexico last week.

The Department of Defense estimates that more than 7,000 troops will be positioned in California, Arizona and Texas in support of the Department of Homeland Security and Customs and Border Protection. In which case, the border mission, dubbed Operation Faithful Patriot, will have a larger U.S. military footprint than the combined efforts in Iraq and Syria. However, last week, Trump said he was prepared to deploy as many as 15,000 service members to the border, a move that would be on par with the U.S. troop presence in Afghanistan, which remains America's longest war. -CNBC

The Washington Post had previously estimated the cost of deployment at $200 million by the end of the year.

During a Saturday campaign rally in Montana, President Trump said "Mexico is trying, they are trying but we’re different, we have our military on the border," adding "And I noticed all that beautiful barbed wire going up today. Barbed wire, used properly, can be a beautiful sight."

TRUMP: “Barbed wire used properly can be a beautiful sight." pic.twitter.com/BFuc3ljwfo — JM Rieger (@RiegerReport) November 3, 2018

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The original caravan continued on foot Saturday after Mexico rescinded an offer to bus them to Mexico City, citing a lack of water. They are currently making their way through the Gulf Coast state of Veracruz, and are around 750 miles from the US border. The caravan's numbers have dropped from 7,000 to around 4,000 over the last few weeks, while around 3,000 have applied for asylum in Mexico and others haver returned home.

On Friday night, Veracruz governor Miguel Ángel Yunes offered bus rides to the country's capital, however he quickly rescinded the offer, blaming maintenance work on Mexico City's water supply which he said left 7 million people without water over the weekend.

Mexican officials, meanwhile, have ceased to provide bus, truck and van rides to the group.