"The USA PATRIOT Act broadened the permissible circumstances for the use of the military to assist law enforcement agencies in countering terrorism," the report states, "but Congress also reaffirmed its determination to maintain the principle of the posse comitatus law. The perceived breakdown in civil law and order in Hurricane Katrina's wake evoked more calls to reevaluate the military's role in responding to disasters."
Despite those calls, the report says the Posse Comitatus Act has remained largely unchanged since it passage, though plenty of exceptions exist, too - such as one that allows the armed forces to be used in response to an insurrection. The California National Guard turned out in 1992 after the acquittal of Los Angeles police officers who beat motorist Rodney King led to angry riots in the streets.
In 2002, after the Sept. 11 attacks, then-President George W. Bush created the U.S. Northern Command to aid civil authorities, and it's done so on numerous occasions just this year. Air Force jets flew over the recent Republican National Convention in Florida for added security, while Black Hawk helicopters were dispatched to help if needed with search-and-rescue efforts during Hurricane Isaac.
The Center for Investigative Reporting, California Watch's parent organization, has examined in articles over the last year whether the perception of a new threat landscape has caused local police to become overly militarized. A December story explored the hundreds of millions of dollars in federal homeland security grants used partly by state and local law enforcement since Sept. 11 to purchase combat-style gear, including armored trucks and tactical attire. A March story described millions in surplus military equipment given to police in California, more during 2011 than any other time since Congress created the program for cast-off Pentagon goods in the 1990s.
However, debate over the Posse Comitatus Act dates back to well before Sept. 11, according to the report.
Political activists during the 1970s successfully fought off a prosecution attempt by arguing that the Posse Comitatus Act prohibited the military from becoming involved in a dispute over the treatment of Native Americans. Members of the American Indian Movement occupied a village on South Dakota's Pine Ridge Reservation, and troops were called to provide assistance. The incident eventually led Congress to pass a law allowing the military to aid police on a limited basis with equipment and information.
The governor of California in 1877 requested federal troops when railroad strikers - resentful of Chinese immigrant workers - began to cause disturbances. They were called upon again during the California Gold Rush when vigilantes attempted to take on increased lawlessness themselves.
"It's important that there are clear distinctions between what is acceptable and what is not," said George Foresman, a former undersecretary at the Department of Homeland Security. "When the military is used - whether the decision is made by the president or governor - there has to be an intimate understanding of Posse Comitatus, and unfortunately, this is not the case. Frankly, this CRS report is a document that every key decision-maker or adviser should keep in their bottom desk drawer as a reference, just above their resignation letter. If they don't, the resignation letter might be the next document they need."
Reports from the Congressional Research Service technically are not public and are compiled at the request of Washington lawmakers and their Capitol Hill staffers. Many of the reports wind up in public hands, anyway - think tanks and academics value their nonpartisan tone and insight.
No indication was given as to why the most recent report on the Posse Comitatus Act was requested, but members of Congress often seek in-depth legal backgrounds to prepare them for committee hearings and crafting new legislation.
Read more California investigative reports at CaliforniaWatch.org.