The U.S. military is the most effective fighting force in history — so effective, in fact, that politicians and pundits have come to see it as a panacea for every security problem posed by the terrorist threat. But on the home front there are many tasks for which the military is ill‐​suited and where its deployment would be ineffective and dangerous.

Nowhere is that clearer than with the growing calls to militarize our borders. Politicians like Rep. Tom Tancredo (R.-Colo.) and Sen. Trent Lott (R.-Miss.) and conservative pundits like Bill O’Reilly and Michelle Malkin want armed soldiers to enforce U.S. immigration law. In her new bestseller Invasion: How America Still Welcomes Terrorists, Criminals, and Other Foreign Menaces to Our Shores, Malkin writes that “at the northern border with Canada… every rubber orange cone and measly ‘No Entry’ sign should immediately be replaced with an armed National Guardsman.” She suggests that something in the neighborhood of 100,000 troops might be appropriate.

The problem with this idea is that the same training that makes U.S. soldiers outstanding warriors makes them extremely dangerous as cops. Lawrence Korb, former assistant secretary of defense in the Reagan administration, put it succinctly: The military “is trained to vaporize, not Mirandize.”

No one knows this better than the military establishment, which is why the Pentagon has consistently resisted calls to station troops on our borders, most recently in the spring of last year, when Congress pushed for border militarization. Pentagon officials raised the possibility of an “unlawful and potentially lethal use of force incident” if the troops were armed. Ultimately, some 1,600 National Guardsmen were placed at the Mexican and Canadian borders for a six‐​month mission, most of them unarmed. A Pentagon official told United Press International, “We don’t like to do these things. We do them as a matter of last resort. That’s why we entered into this undertaking with a specific end date and a specific requirement.”

The Pentagon was right to worry. U.S. troops have been placed on the borders in the past, as part of the quixotic fight against drug smuggling. Even though those deployments have been limited to surveillance and support roles, they’ve led to tragedy. In 1997, a Marine anti‐​drug patrol shot and killed 18‐​year‐​old high school student Esquiel Hernandez, who was carrying a .22 caliber rifle while tending goats on his own farm in Redford, Texas near the Mexican border. The Justice Department paid out $1.9 million to the Hernandez family as settlement of a wrongful death lawsuit.

The Hernandez incident should be a cautionary tale for those who seek to militarize our borders. An internal Pentagon investigation of the incident noted that the soldiers were ill‐​prepared for contact with civilians, as their military training instilled “an aggressive spirit while teaching basic combat skills.”

Because of the restrictions imposed by the Posse Comitatus Act, the federal law that proscribes the military from “executing the laws,” the Marines who killed Hernandez operated under rules of engagement that prevented them from arresting or otherwise directly engaging civilians. Nonetheless, according to a senior FBI agent involved with the case, “The Marines perceived a target‐​practicing shot as a threat to their safety… From that point, their training and instincts took over to neutralize a threat.” The camouflaged Marines tailed Hernandez for 20 minutes, and failed to identify themselves or try to defuse the situation. When Hernandez raised his rifle again, a Marine shot him, and let him bleed to death without attempting to administer first aid.

The new proposals to use troops for border patrol work would greatly multiply the dangers revealed by the Hernandez incident. Unlike the soldiers deployed for the drug war, the troops on border patrol duty would be given arrest authority and allowed to directly engage civilians. The danger to civilians wouldn’t be limited to border areas either, given that federal law allows the Border Patrol to set up checkpoints as far as 100 miles inland from the border or shoreline.

Having the military enforce the immigration laws isn’t wise, it isn’t necessary, and it’s not legal. Both the INS and the Border Patrol are getting a half a billion dollar infusion of new resources, and rapidly hiring new agents. If still more border patrol personnel are needed, they should be hired. But border security can be provided without eroding America’s tradition of civil‐​military separation.