Even the most casual expression of doubt about the war could trigger a beating by a mob, and the humiliation of being made to kiss the flag in public. Americans who declined to buy Liberty Bonds (issued by the Treasury to finance the war) sometimes awoke to find their homes streaked with yellow paint. Several churches of pacifist sects were set ablaze. Scores of men suspected of disloyalty were tarred and feathered, and a handful were lynched. Most of the violence was carried out in the dark by vigilantes who marched their victims to a spot outside the city limits, where the local police had no jurisdiction. Perpetrators who were apprehended were rarely tried, and those tried were almost never found guilty. Jurors hesitated to convict, afraid that they too would be accused of disloyalty and roughed up.

Both Creel and Wilson privately deplored the vigilantes, but neither acknowledged his role in turning them loose. Less violent but no less regrettable were the actions taken by state and local governments and countless private institutions to fire German aliens, suspend performances of German music, and ban the teaching of German in schools.