Rummy's posse: Pentagon police work.

• Author: Welch, Matt
• Position: Donald H. Rumsfeld, Posse Comitatus Act

IN 1878 Congress passed the Posse Comitatus Act, barring "participation by a member of the Army, Navy, Air Force, or Marine Corps in a search, seizure, arrest, or other similar activity" on United States soil unless specifically authorized by law. Army troops sent to discourage insurrection in the post Civil War South were engaging in classic mission creep, enforcing workaday laws that would be more appropriately handled by town sheriffs, perhaps with the assistance of ad hoc "posses" drawn from local citizens. The act was intended to restore the armed forces to their proper task of defending the United States from external threats.

Over the years, exemptions have been added. But the main thrust of the law--keeping the four fighting branches of the military away from American citizens--has stood firm. Until now.

In June 2005, the Defense Department approved a sweeping new reorientation, called "The Strategy for Homeland Defense and Civil Support," that will (in the document's own words) "fundamenttally change the Department's approach to homeland defense in an historic and important way." The military now will take a "lead role" in "execut[ing] military missions" on American soil to "dissuade, deter, and defeat attacks."

A key part of that lead role--and the most likely way this new strategy will affect...