Nearly immediately, Stephens faced controversy regarding the Preparedness Day Bombing, a terrorist attack on the San Francisco Preparedness Day parade on July 22, 1916. The attack was blamed on left wing radicals, in particular union leader and former Industrial Workers of the World member Thomas Mooney, and his alleged accomplice, Warren Billings. Both Mooney and Billings were convicted, though critics said later that the trial was conducted in a lynch mob atmosphere. Governor Stephens supported both convictions. However, international sympathy for Mooney quickly spread, making him one of the United States's most famous political prisoners. There was national and international pressure on Stephens to intervene for Mooney. President Woodrow Wilson personally telegraphed Stephens to ask him to review the case against Mooney. Stephens yielded, but only slightly, commuting Mooney's death sentence to life imprisonment.