Federal authorities arrested three men allegedly linked to a violent white-supremacist group who had discussed traveling to a pro-gun rally Monday in Richmond, Va., and preparing for a possible race war, according to a law-enforcement official. Two of the men, one a former Canadian Army reservist in the U.S. illegally, face charges including transporting a firearm and ammunition with intent to commit a felony, according to the U.S. attorney’s office in Maryland. One was also charged with transporting a machine gun, and the third man was charged with transporting and harboring an illegal alien. Online court records didn’t list attorneys...