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Amidst calls to use the military to fight the war on terrorism at home, some experts warn that allowing the military to perform a domestic role would set a dangerous precedent, put civilians at unnecessary risk and threaten Americans' basic civil liberties.

"The military has been so impressive abroad that in many ways, it's not surprising that some people think it could be equally effective at fighting the war at home," said Gene Healy, senior editor at the Cato Institute (search).

But, Healy added, those people could find themselves sadly mistaken.

"A free society is not a militarized society. It is a society where law enforcement is the duty of civilians and any effort to change that ought to meet a very heavy burden of proof," he said.

A number of politicians have been talking about making such a change. Rep. Tom Tancredo, R-Colo., and Sen. Trent Lott, R-Miss., have been calling for a militarization of America's borders.

Since Sept. 11, 2001, President Bush has called for reviewing the Posse Comitatus Act (search), which restricts the domestic role of the military. Other administration officials, including Deputy Defense Secretary Paul Wolfowitz and Homeland Security Secretary Tom Ridge have made similar suggestions. Gen. Ralph E. Eberhart, head of the new Northern Command, which oversees all military forces in America, has also called for a fresh review.

Enacted in 1878, Posse Comitatus originally referred to a sheriff's common law power to call on the male population of a county to enforce the laws. The act bars law enforcement officials from calling on military personnel for that purpose.

But the law includes many exceptions. It only applies to troops operating under federal command. Therefore, the National Guard can be called up by state governors to enforce laws. Under the law, the Army is also permitted to provide training and equipment to law enforcement agents. In fact, the military is barred only from hands-on policing — enforcing laws, making arrests and other police duties.

Under the act, which Congress is able to amend, if America is imperiled by a military threat, U.S. troops can respond. Experts have cited a modern-day Pancho Villa or an Al Qaeda-backed kamikaze pilot as examples in which the military could be used to respond to a threat on American soil.

Since Sept. 11, the military has increasingly been recruited for duties on domestic turf. Immediately after the terrorist attacks, jets patrolled the airspace above New York and Washington, D.C., and were given authority to shoot down commercial airliners.

In 2002, the Pentagon temporarily deployed troops on the borders with Canada and Mexico. In February of that year, thousands of troops backed up by Black Hawk helicopters patrolled Salt Lake City, providing security for the Winter Olympics.

Supporters of using the military to guarantee domestic security say that in an age of terror, regular police are not equipped to perform the tasks needed to beat back terrorists.

Police "lack the technical capability. Police officers are trained to be restrained with their application of force and try to avoid firing their weapons if possible. This is good because we want a restrained police force," said David Klinger, a professor of criminology at the University of Missouri-St. Louis (search). "I don't want the police to adopt the military mindset. The military basically kills people and blows things up. I don’t want the police to do that."

That said, Klinger added that because of this training and mentality, it is very difficult for police "to defeat well-equipped aggressors.

"[Terrorists] have engaged us in war on our soil, and in my opinion, the proper response is to call out the warriors to get them. Let us give the people who have sworn to protect us the authority to do so," said Klinger, who was a patrol officer for the Los Angeles and Redmond, Wash., police departments.

But civil libertarians argue that using the military at home can have disastrous consequences. For instance, during World War I, the military crushed employee strikes and was involved in domestic spying. Healy said the military launched millions of investigations against private citizens because of their political beliefs and positions against the war. This dragnet ended up catching only one German spy, he said.

"The Army is a blunt instrument. We're fighting an asymmetric war against an enemy amongst us," Healy said. What is needed is "investigative skills, not overwhelming firepower."

Former Republican Rep. Bob Barr of Georgia, now a civil liberties advocate, also warned about the consequences of "blurring the line between domestic law enforcement and military action," citing the 1993 Justice Department military-style assault on the Branch Davidian compound in Waco, Texas, which left more than 80 civilians dead.

"The federal government is encouraging the militarization of local police forces by giving weaponry and providing advisers. By militarizing law enforcement, we will end up with a very different country," Barr said. "Do we want to live in a society when military aircraft are scrambled and used to go after serious domestic threats?"

But since the terror attacks, fresh calls have been made for the military to do some police work.

"The pressure is building and has been building since September 11 to give the military a greater domestic role," Healy said. "In the American tradition, use of the military domestically is a last resort. It is not a first responder and we need to keep it that way."