Question: Did Lincoln ever fight a duel?
Almost. In 1842, Lincoln wrote a series of anonymous letters published in the Sangamo Journal mocking prominent Democrat James Shields, the Illinois State Auditor. After Mary Todd (to whom Lincoln had been engaged the year before) and Julia Payne wrote a similar letter, Shields demanded that the editor reveal the identity of the author. Upon learning that Lincoln had written the letters, Shields challenged him to a duel. Lincoln, who was always awkward with women, mustered a rare show of gallantry and made no mention of Mary's involvement in writing one of the letters.
Since Shields was the challenger, Lincoln had the privilege of naming the conditions for the contest. He proposed the ludicrous spectacle of a fight with "Cavalry broad swords of the largest size" while standing in a square ten feet wide and about twelve feet deep, which would put the much shorter Shields at a serious disadvantage. Lincoln may have hoped that the silliness (as well as the danger) of the proposed contest would bring Shields to his senses, but both men went ahead with their preparations for the duel until their seconds managed to arrange a peaceable settlement. Lincoln afterwards was embarrassed by the incident and rarely spoke of it.