The recent uproar over armed EPA agents descending on a tiny Alaska mining town is shedding light on the fact that 40 federal agencies – including nearly a dozen typically not associated with law enforcement -- have armed divisions. The agencies employ about 120,000 full-time officers authorized to carry guns and make arrests, according to a June 2012 Justice Department report. Though most Americans know agents within the Drug Enforcement Agency and the Federal Bureau of Prisons carry guns, agencies such as the Library of Congress and Federal Reserve Board employing armed officers might come as a surprise. The incident...