Kenneth Melson of the U.S. Bureau of Alcohol, Tobacco and Firearms faces controversy over the agency's surveillance program that allowed U.S. guns into Mexico. He is said to be eager to testify to Congress. The acting director of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives is strongly resisting pressure to step down because of growing controversy over the agency's surveillance program that allowed U.S. guns to flow unchecked into Mexico, according to several federal sources in Washington.