The districts that contain Chicago, Los Angeles and New York City ranked last in terms of federal gun law enforcement in 2012, according to a new report from Syracuse University's Transactional Records Access Clearinghouse, which tracks federal data.

Federal gun crimes include illegal possession of a firearm in a school zone, illegal sale of a firearm to a juvenile, felon, or drug addict, and illegal transport of a firearm across state lines. In Chicago, the majority of gun charges last year were for firearms violations.

The districts of Eastern New York, Central California, and Northern Illinois ranked 88th, 89th and 90th, respectively, out of 90 districts, in prosecutions of federal weapons crimes per capita last year, but it wasn't always this way. All three districts fell lower on the list than they had been in years past. In 2010, for example, Chicago was 78th in federal weapons prosecutions.

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These cities also have some of the nation's most restrictive gun laws, as well as the most active mayors in championing gun control. New York Mayor Michael Bloomberg, Chicago Mayor Rahm Emanuel and Los Angeles Mayor Antonio Villaraigosa are all members of the national Mayors Against Illegal Guns campaign.

D.C., which also has tough gun laws, was in the lower half of the list in 2012, coming in at 78th. In 2011, D.C. prosecuted a higher number of gun crimes, coming in at number 49.

National Rifle Association chief Wayne LaPierre first pointed to the report on Meet the Press Sunday, when he demanded to know why the national press corps wasn't asking the White House or U.S. attorneys general to explain lax federal enforcement of gun laws.

His comment didn't sit well with gun control activists, including the group Moms Demand Action For Gun Sense In America. "It's like, 'don't look at us, look at gun enforcement'," says the group's founder Shannon Watts. "But the NRA works to block gun prosecutions all the time."

Requests for comment from the U.S. Attorney's offices in New York and California were not immediately returned. But the U.S. attorney's office in the Northern District of Illinois maintains that federal weapons law enforcement is among the top priorities of their office. "We have a number of different methods of attacking gangs, guns, drugs and violent crime," says spokesman Randall Sanborn, who notes that many gun arrests are reviewed to determine whether the arrest should stay with the county or be brought to the federal level. "We look at which court the defendant is likely to get a substantially greater sentence... More cases that used to be brought federally are now staying in state courts because [they are] now able to get a sentence equally great or greater," he says.

The TRAC report notes that many more gun arrests happen at the state and local level than happen at the federal level, and that it's difficult to assess how many prosecutions happen overall.

While the districts that ranked lowest last year for federal gun crime prosecutions all contained major cities, the districts at the top of the list for its enforcement were almost exclusively rural. The districts of Southern Alaska, Kansas and Western Tennessee ranked first, second and third in prosecutions of federal weapons laws per capita last year.

Susan Long, a statistician and co-director of TRAC, said the data revealed a stronger federal enforcement presence in rural areas than urban ones. "If taxpayers of [a certain area] don't pass strong gun control measures ... the feds pick up the ball," she said. "But now we've got sequestration cutting back on all these resources."

The U.S. court system has said that sequestration will have a major impact on the federal judiciary, including the furlough of some court employees, cuts to the federal defenders' office and fewer probation officers for criminal offenders.