On October 14, 1912, former saloonkeeper John Flammang Schrank (1876–1943) attempted to assassinate former U.S. President Theodore Roosevelt while he was campaigning for the presidency in Milwaukee, Wisconsin. Schrank's bullet lodged in Roosevelt's chest after penetrating Roosevelt's steel eyeglass case and passing through a thick (50 pages) single-folded copy of the speech titled "Progressive Cause Greater Than Any Individual", which he was carrying in his jacket. Schrank was immediately disarmed (by Czech immigrant Frank Bukovsky) and captured; he might have been lynched had Roosevelt not shouted for Schrank to remain unharmed. Roosevelt assured the crowd he was all right, then ordered police to take charge of Schrank and to make sure no violence was done to him. Roosevelt did not believe in police harming civilians.

As an experienced hunter and anatomist, Roosevelt correctly concluded that since he was not coughing blood, the bullet had not reached his lung; he declined suggestions to go to the hospital immediately. Instead, he delivered his scheduled speech. His opening comments to the gathered crowd were, "Ladies and gentlemen, I don't know whether you fully understand that I have just been shot, but it takes more than that to kill a Bull Moose."

Afterwards, probes and an x-ray showed that the bullet had lodged in Roosevelt's chest muscle, but did not penetrate the pleura. As doctors concluded that it would be less dangerous to leave it in place than to attempt to remove it, Roosevelt carried the bullet with him for the rest of his life. Both President William Howard Taft and Democratic nominee Woodrow Wilson suspended their own campaigning until Roosevelt recovered and resumed his. When asked if the shooting would affect his election campaign, he said to the reporter "I'm fit as a bull moose." The bull moose became a symbol of both Roosevelt and the Progressive Party; it often was referred to as simply the Bull Moose Party. He spent two weeks recuperating before returning to the campaign trail. He later wrote a friend about the bullet inside him, "I do not mind it any more than if it were in my waistcoat pocket."

The shooter, John Schrank, initially pleaded guilty to the charge of attempted murder, but the trial judge, unconvinced of Schrank's sanity, declined his plea and the case was brought to trial. Schrank was found not guilty by reason of insanity by the jury and was sentenced to indefinite institutionalization.