TUCSON, Ariz. - Federal agents were worried that the gun used to shoot Rep. Gabrielle Giffords (D-Ariz.) in the head could have been part of the controversial “Fast and Furious” gun-tracking operation. They learned eventually that it had not, sources said. The “Fast and Furious” operation was a program run by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) that authorized and monitored the sale of weapons to known and suspected straw purchasers for Mexican drug cartels with the stated goal of exposing and dismantling gun trafficking routes. House Oversight and Government Reform Committee Chairman Darrell Issa (R-Calif.) held...