As its overwhelming victories in Afghanistan and Iraq have demonstrated, the U.S. military is the most effective fighting force in human history. It is so effective, in fact, that many government officials are now anxious for the military to assume a more active policing role here at home.

Deploying troops on the home front is very different from waging war abroad. Soldiers are trained to kill, whereas civilian peace officers are trained to respect constitutional rights and to use force only as a last resort. That fundamental distinction explains why Americans have long resisted the use of standing armies to keep the domestic peace.

Unfortunately, plans are afoot to change that time-honored policy. There have already been temporary troop deployments in the airports and on the Canadian and Mexican borders and calls to make border militarization permanent. The Pentagon has also shown a disturbing interest in high-tech surveillance of American citizens. And key figures in the Bush administration and Congress have considered weakening the Posse Comitatus Act, the federal statute that limits the government’s ability to use the military for domestic police work.

The historical record of military involvement in domestic affairs cautions against a more active military presence in the American homeland. If Congress weakens the legal barriers to using soldiers as cops, substantial collateral damage to civilian life and liberty will likely ensue.