Role of U.S. military at border guided by Civil War-era law

The recent arrival of U.S. military forces at the southern border to bolster U.S. Customs and Border Protection agents raises questions about the role of the military to quell domestic and border disturbances, such as those that recently took place in Tijuana, Mexico.

The Nov. 25 confrontation spotlighted the 1878 Posse Comitatus Act, a Reconstruction-era law that restricts military forces from enforcing U.S. law. A new ABA Legal Fact Check traces the history of using troops to enforce civil authority and explores the legal limits set forth by the 140-year old law and its revisions.

Prior to the passage of the PCA, as the law is called, presidents faced few limits on using U.S. troops to enforce law domestically. Perhaps the broadest campaign involving the military on U.S. soil was during the Civil War era, when Union troops became the primary form of law enforcement in the South.

The PCA now expressly allows military action to suppress insurrection or to enforce federal authority. And over the years, presidents have relied upon these exceptions at critical moments in American history.

In the early days of the civil rights movement, for instance, then-President Dwight D. Eisenhower used troops in September 1957 to force the city of Little Rock, Ark., to desegregate its schools after mobs prevented African-American students, known as the Little Rock Nine, from attending Little Rock Central High School. When the Arkansas Army National Guard refused to enforce the federal court order to integrate, Eisenhower sent the 101st Airborne Division to end the standoff.

Last month’s While House “cabinet order” sending about 5,800 troops to the southern border to assist U.S. Customs and Border Protection agents is the most recent example of U.S. troops bolstering civil authorities. As the ABA Legal Fact Check suggests, the military can legally assist border agents in these situations although there are limits on what it can do.

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