Under President Johnson, US involvement in Vietnam escalated through bombing campaigns and increasing troop levels despite doubts about winning. The 1964 Gulf of Tonkin incident led to greater war powers for Johnson. The 1968 Tet Offensive saw major attacks on South Vietnamese cities and turned US public opinion against the war. Protests against the war grew larger along with revelations of atrocities like the My Lai massacre. The draft system led many American men to avoid service or flee to Canada to avoid fighting in Vietnam.