That was 'the date on which Lincoln asked to be released from his engagement to Mary Todd'. In the book Lincoln's Preparation for Greatness: The Illinois Legislative Years, Paul Simon has a chapter covering the period, which Lincoln later referred to as 'The Fatal First', or January 1, 1841. Lincoln is believed to have suffered something approaching clinical depression. This was at the same time as the collapse of a legislative program he had supported for years, the permanent departure of his best friend, Joshua Speed, from Springfield, Illinois, and the proposal by John Stuart, Lincoln's law partner, to end their law practice. In what historian Allen Guelzo calls 'one of the murkiest episodes in Lincoln's life,' Lincoln called off his engagement to Mary Todd. Lincoln and Mary Todd met in Springfield in 1839 and became engaged in 1840.
