Aziz didn't respond and instead helped arrange a press conference. When the Wall Street Journal highlighted the episode in a story about domestic intelligence gathering by the military, the Army's Intelligence and Security Command acknowledged that the agents "exceeded their authority" and introduced "refresher training" on the limits of the military's jurisdiction.

As it turns out, though, it may be the public that needs a refresher course on the role of its military forces. In 2002, the Defense Department updated its Unified Command Plan, which made the already blurry lines between civilian and military even less legible. Since then, all over America, law enforcement and intelligence agencies have been making information about the public available to a Pentagon power center most people have never heard about: U.S. Northern Command, or NORTHCOM, located at Peterson Air Force Base in Colorado Springs. Hidden deep inside Cheyenne Mountain, more than 100 intelligence analysts sift through streams of data collected by federal agents and local law en- forcers–continually updating a virtual picture of what the command calls the North American "battlespace," which includes the United States, Canada, and Mexico, as well as 500 miles out to sea. If they find something amiss, they have resources to deploy in response that no law enforcement agency could dream of. They've got an army, a navy, an air force, the Marines, and the Coast Guard.

The creation of NORTHCOM, as part of the "unified plan" in the wake of 9/11, established the military's first domestic combatant command center. This precedent departs from a long-standing tradition of distinguishing between the responsibilities of the military and those of law enforcement. Since 1878, when Congress passed the Posse Comitatus Act in response to interference in elections by federal troops, an underlying assumption of U.S. democracy has been that soldiers should not act as police officers on American soil. While the Chinese army might send tanks to Tiananmen Square and the Liberian military might man checkpoints in the capital, the presence of National Guardsmen, carrying firearms and dressed in camouflage, patrolling American territory in the weeks after 9/11 was a striking anomaly.

The new NORTHCOM is designed to take command of every National Guard unit in the country, as well as regular troops, and wield them as a unified force. It has a variety of jobs, including fighting the war on drugs and supporting civilian authorities in cases of natural disaster, civil disorder, or terrorist attack. But it also has the less straightforward task of locating terrorists before they strike, which means, first and foremost, coordinating intelligence work. To this end, the command has been forging a national surveillance system directly linking military intelligence operations to local law enforcement intelligence operations and private security and information companies. These partnerships allow the military to skirt federal privacy laws that restrict its ability to maintain files on ordinary people–prohibitions that apply to the Pentagon but not to private data miners, such as ChoicePoint and LexisNexis Group, or state and local police departments. In addition, personal data is culled from public records, confidential sources, and other repositories routinely cultivated by more than 50 government agencies. For example, NORTHCOM taps into one law enforcement intelligence-sharing network into which local, state, and federal law enforcement can upload information on individuals they've surveilled.

Because most of its activity takes place in secret, and because the Pentagon has still not fully clarified its mandate, very little is known about exactly what kind of information NORTHCOM is gathering, and on whom. A review of documents and interviews with military and civil liberties experts makes clear, however, that the command's domestic intelligence ambitions are more far-reaching than anything the U.S. military has undertaken in the past and that the hope is to "fuse" disparate government databases so they can be readily accessed by NORTHCOM's leadership.

Not surprisingly, all of this worries civil liberties advocates. "There is no explicit prohibition in any law to the effect that the Pentagon may not engage in domestic intelligence," says Kate Martin, director of the Center for National Security Studies in Washington, D.C. To place a wiretap or to search a home of a suspected terrorist without their knowledge, Martin notes, officials need a secret warrant from an intelligence court–but other than that, they have a great deal of leeway. "The military can follow you around," she notes. "It can use giant, secret databases of linked networks to gather a picture of the activities of millions of Americans, mapping all of their associations, and the only restriction is that such surveillance be done for purposes of foreign intelligence, counterterrorism, the drug war, or force protection."

Indeed, to beef up protection of its "battlespace," the new command also includes "influence operations specialist[s]," who work on psy-ops "themes" and "deception plans," as first reported in Congressional Quarterly last year. Although the category of "enemy combatant" muddies old definitions of foreign and domestic subjects, NORTHCOM spokesman Sean Kelly assured Mother Jones in an email that the command draws "distinctions between domestic operations and operations conducted outside of U.S. territory.... The idea that the American public would ever be the target of psychological operations or deception by NORTHCOM is completely inconsistent with U.S. law and our mission."

Critics of NORTHCOM say they recognize the need to protect America from terrorist attack, but argue that the delicate task of domestic intelligence gathering should be left to law enforcement. Military affairs expert William Arkin–who recently broke the news that NORTHCOM had established a set of domestic commando teams who were, among other things, deployed at President Bush's inaugural–observes that "once you cross the threshold of believing that databases are going to reveal illegal behavior, it is only steps away from getting into the business of domestic intelligence…and supplanting the role of the National Guard, which has traditionally been in charge of domestic security."

Concern about NORTHCOM's expanding powers is not limited to civil liberties watchdogs. Former CIA lawyer Suzanne Spaulding was the executive director of the National Commission on Terrorism under L. Paul Bremer III in 2000 and now works as a national security consultant. She worries that military intelligence services won't always distinguish between people who are fair game–such as foreign terrorists–and ordinary people who are going about their lives with an expectation of privacy. "People will say, 'Hey, wait a minute, you can't do that!'" she says. "And the military may say, 'This is not law enforcement, this is a military operation against a group of enemy combatants.'" She points out that constitutional safeguards against surveillance of individuals by law enforcement may apply differently to defense activities under NORTHCOM. "This issue needs discussion and debate," she says, "and the public ought to know about it."

More troubling than being watched, though, is what might happen after the spying is over. NORTHCOM is still prohibited from doing much of the work police departments and the FBI do, but it could end up doing work that its parallel commands do overseas. Joseph Onek of the Constitution Project in Washington, D.C., a bipartisan nonprofit focused on civil liberties during wartime, puts it this way: "We're worried that some hotshot military intelligence guy gets back from the Middle East and goes to work with NORTHCOM, using some of the same interrogation methods used at Abu Ghraib and Guantanamo Bay."