Military planners anticipate that only a small percentage of Central American migrants traveling in the caravans President Trump characterizes as “an invasion” will reach the U.S. border, even as a force of more than 7,000 active-duty troops mobilizes to prevent them from entering the United States.

According to military planning documents, about 20 percent of the roughly 7,000 migrants traveling through Mexico are likely to complete the journey. The unclassified report was obtained and published by Newsweek on Thursday. If the military’s assessment is accurate, it would mean the United States is positioning five soldiers on the border for every one caravan member expected to arrive there.

“Based on historic trends, it is assessed that only a small percentage of the migrants will likely reach the border,” the report says. It was prepared by U.S. Army North, a component of U.S. Northern Command, which oversees the mission dubbed Operation Faithful Patriot.

As a migrant caravan, with an estimated 2,300 children, makes its way to the border, a parent and a boy explain why they're making the trek. (Drea Cornejo, Julia Galiano-Rios/The Washington Post)

The assessment also indicates military planners are concerned about the presence of “unregulated armed militia” groups showing up at the border in areas where U.S. troops will operate.

The Washington Post was unable to independently confirm the report’s authenticity. Reached Friday, military officials did not dispute its veracity but declined to address questions about its contents.

Seizing on immigration as his main campaign theme ahead of Tuesday’s midterm elections, Trump has depicted the caravans — at least four have formed, though they remain hundreds of miles away — as a grave danger to U.S. national security, claiming they are composed of “unknown Middle Easterners,” hardened criminals and “very tough fighters.” He also insists the number of migrants heading north is much larger than estimates put forward by U.S. and Mexican governmentofficials.

President Trump slammed the "tough people" in the migrant caravan on Nov. 1, and said his administration will not "let them in." (The Washington Post)

The military assessment does not support any of those claims.

The report, dated Oct. 27, notes that caravan members are unlikely to arrive for at least two to four weeks. Among those traveling are “limited #s of Bangladeshi, Haitian and African individuals,” it reads. It makes no mention of Middle Eastern countries.

Homeland Security officials say they have identified 270 individuals in the caravan with “criminal histories, including known gang membership.” In a statement, the department also said foreign nationals from 20 countries are among the groups, though none of the nations it listed are in the Middle East.

In the military planners’ most likely scenario, the caravans will continue to dwindle in size as they move north with “no terrorist infiltration,” potentially causing a “balloon effect” on smuggling activity as traffickers attempt to exploit the diversion created by Trump’s focus on the migrants.

In its “most dangerous” assessment, the caravan would “grow markedly” and become exploited by terrorists and traffickers, leading to increasing “cross border engagements.” The assessment does not assign a numerical probability to those scenarios.

Trump said this week that he wants to send as many as 15,000 troops to the border to prepare for the caravans. The deployment appears to be the largest such peacetime mobilization of active-duty U.S. troops at the border in at least a century.

High on the list of potential dangers facing U.S. personnel, according to the military’s assessment, is the presence of “unregulated militia members self-deploying to the border in alleged support” of U.S. Customs and Border Protection. It estimates that 200 militia members could show up while troops are in the area.

“They operate under the guise of citizen patrols,” the report reads, warning of “incidents of unregulated militias stealing National Guard equipment during deployments.”

The assessment does not go into further detail about those incidents, but Border Patrol officials have also warned landowners in the area about the possibility of gun-carrying militias on their property in the coming weeks.

Protesters and “anarchists” arriving along the border also pose a risk, according to the report. “Previous protests in support of immigration caravans or enforcement of immigration law have occurred throughout the U.S.,” it says. “Normally peaceful unless extreme right or left groups attend.”

Dan Lamothe contributed to this report.