Robert M. Goldman, "Davis, David," American National Biography Online, February 2000, http://www.anb.org/articles/11/11-00219.html.
During his fourteen-year tenure on the [Supreme] Court Davis participated in several notable decisions. That for which he is best remembered is the Court's 1866 ruling in Ex parte Milligan. In September 1862, President Lincoln had issued a proclamation suspending the writ of habeas corpus for civilian prisoners in the North under military authority. Such persons could be arrested for resisting the draft, obstructing volunteers, or other acts of disloyalty. Moreover, such individuals could be tried and punished by courts-martial or military commission. Lambdin P. Milligan, leader of the Sons of Liberty, an Indiana Copperhead group opposed to the war, was tried and convicted by a military commission based on the proclamation. Overturning Milligan's conviction, Davis held that Lincoln's suspension of the writ of habeas corpus had been an unconstitutional usurpation of congressional authority and that the president had no authority to authorize the use of military courts except in case of controlling necessity. Although Davis received harsh criticism from Republicans for this decision, he believed it an important statement of civil liberties protection.