It was August 2004 in New York City and President George W. Bush was in town, attending the Republican National Convention at Madison Square Garden. Thousands of protesters were out in the streets in the sweltering summer heat, carrying placards emblazoned with slogans like “Push Bush Out The Door” and “The War on Terror is A Lie.” As the demonstrations rumbled on outside, the National Security Agency was getting to work on an unusual operation. The agency, which mostly focuses on vacuuming up communications and monitoring events in foreign countries, had been drafted in to provide surveillance support to other federal agencies. A month earlier, in late July 2004, the NSA had served a similar role — using its vast electronic spying apparatus to bolster security at the Democratic National Convention in Boston. That’s according to a classified NSA document, published Monday by The Intercept, which offers a rare glimpse into the little-known circumstances surrounding the agency’s domestically focused missions.

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The NSA became involved after then-Homeland Security Secretary Thomas Ridge and Attorney General John Ashcroft declared the conventions to be “National Special Security Events.” This designation came into existence following a secret directive issued in May 1998 by then-President Bill Clinton. The directive ensured that major gatherings of national or international significance would receive special federal resources to boost security, “with the goal of preventing terrorist attacks and criminal acts,” the classified NSA document explains. Between September 1998 and February 2008, there were 28 events approved for this extra level of protection, U.S. Department of Transportation records show. These included — aside from Republican and Democratic conventions — Super Bowls, presidential inaugurations, State of the Union addresses, and the Winter Olympics in Salt Lake City. It is not known whether NSA provided support to all of these events, but previous reporting — and a document published by The Intercept — have revealed that NSA was involved in carrying out surveillance at the Salt Lake City Olympics, where it worked with the FBI in a “fusion cell” known as the Olympics Intelligence Center. The targets of NSA’s surveillance during the 2004 conventions — and whether they were foreigners, Americans, or both — are not disclosed in the agency’s documents, which were obtained by The Intercept from the whistleblower Edward Snowden. The documents do specify, however, that six employees from the agency’s Signals Intelligence Directorate were deployed to New York City and Boston for the events, and that their role was to provide “SIGINT [signals intelligence] support to the FBI, the Department of Homeland Security and other national agencies.” NSA staff were equipped with computers that linked them back to the agency’s headquarters in Fort Meade, Maryland. And if they gathered any intelligence they believed concerned a threat, they could get it declassified so that it could be shared with federal, state, and local officials on site who did not have security clearances.

Protesters are arrested at Union Square after attempting to march without a permit on the second day of the Republican National Convention, in New York City, on Aug. 31, 2004. Photo: Paula Bronstein/Getty Images