By Stephen Mihm
President Donald Trump announced last week that he would send troops to guard the U.S.-Mexico border to beef up immigration enforcement. “Until we can have a wall and proper security,” Trump said, “we are going to be guarding our border with our military.”
Trump’s plan raised alarm bells about possible violations of the 19th-century Posse Comitatus Act, which forbids the military from active involvement in civilian law enforcement. At first glance, Trump’s action looks like another instance of his habitual disregard for the rule of law.
The real problem, though, is the law itself. While Trump’s border operation would raise legitimate concerns, the Posse Comitatus Act has a vexed history, one that makes it difficult to invoke. Moreover, loopholes have multiplied over the years. No one has ever been prosecuted for violating it.
The idea that there should be a sharp divide between the military and civilian law enforcement has a long history in the U.S. But that history is ambiguous. It dates to the years before the American Revolution, when the British turned to soldiers to enforce colonial law, an experience that contributed to the final break with the mother country. American patriots addressed the issue in the Declaration of Independence, complaining that Great Britain had sought to “render the Military independent of and superior to the Civil Power.”
The U.S. Constitution imposed several checks on military power, but did not confront the question of whether the armed forces had a role in law enforcement. In 1792, Congress granted federal marshals the power to enlist state militias to enforce the law. This was framed as an extension of the doctrine of posse comitatus, which originated in medieval Britain: the ability of local constables to call up nearby residents for help enforcing the law (the Latin phrase literally means “force of the county.”)
In doing so, Congress failed to establish a clear distinction between the military and civilian law enforcement. In the succeeding decades, marshals began enlisting army troops for this purpose as well. This was done, as one legal scholar has noted, on the grounds that any federal soldier was also simultaneously a civilian. Though clearly an end run around the original law, this legal fiction went unchallenged, and federal marshals began leaning on soldiers in both the militia and regular army to help enforce laws.
After the passage of the Fugitive Slave Act in 1850, federal marshals frequently enlisted soldiers to return runaway slaves to their owners. In 1854, Attorney General Caleb Cushing declared that entire military units could be used for that purpose.
To many in the North, this seemed like a dangerous mingling of military and civilian power, but after the outbreak of the Civil War, Congress blurred those lines still further in the service of different ends. It amended the 1792 law to permit the president to summon the militia or regular army when he deemed it necessary to enforce federal laws.
This tradition continued after the Civil War, with the military occupation of the former Confederacy. During Reconstruction, President Ulysses S. Grant dispatched federal troops to insure implementation of laws meant to protect the rights of African Americans. Soldiers stood guard at polling stations and even arrested members of the Ku Klux Klan.
Reconstruction died after the contested election of 1876, when Democrats negotiated a withdrawal of federal troops from the South in exchange for acceding to the election of Republican Rutherford B. Hayes. Now free to intimidate blacks and their white allies, Democrats reestablished political control over the former Confederacy, and with it, a majority over the House of Representatives.
In 1878, Southern Democrats in Congress managed to secure passage of the Posse Comitatus Act, which barred the use of federal troops in domestic law enforcement. Its bland language notwithstanding, the law’s intent was to prevent Republican presidents from using troops to enforce election laws protecting the rights of African-Americans in the South.
The unsavory origins of the Posse Comitatus Act make it hard to view it as a high-minded stand against military involvement in civil affairs. To make matters even more complicated, the original prohibition and subsequent amendments have been diluted by a number of exceptions.
These exceptions have enabled presidents to deploy federal troops and state militias in ways that erode the distinction between military and civilian authority. In the late 19th century, for example, presidents tapped federal troops to quell labor unrest.
In the 20th century, these exceptions have led to a number of cases where federal soldiers and state militias have been used to enforce laws. These include shameful episodes like President Herbert Hoover’s decision to send military units to Washington to end a largely peaceful 1932 protest by World War I veterans seeking promised payments to help them survive the Great Depression. But the exceptions have also been used to justify the use of federal troops to enforce desegregation in the South during the 1950s.
More recently, Congress has carved out several additional exceptions meant to make it easier to use the military to help police agencies fight drug trafficking.
The exceptions — to say nothing of the fact that no one has ever been prosecuted for violations of the Posse Comitatus Act — highlight the degree to which the law may not be quite the firewall that conventional wisdom would suggest. Its dubious origin in the violent overthrow of Reconstruction only makes matters worse.
Whether or not Trump is acting in good faith — illegal border crossings have declined in recent years — his use of soldiers for immigration enforcement appears consistent with the letter, if not the spirit, of the law.
Stephen Mihm, an associate professor of history at the University of Georgia, is a contributor to Bloomberg View. This column does not necessarily reflect the opinion of Minnesota Lawyer, the Bloomberg View editorial board or Bloomberg LP and its owners.