Norman B. Ferris, "Curtin, Andrew Gregg," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00286.html.
Although not an elected delegate, Curtin attended the Republican convention at Chicago in May 1860, and there he influenced most members of the Pennsylvania delegation to abandon Cameron and join with politicians from several other states in a movement to derail the candidacy of New York Senator William H. Seward, the clear favorite for the presidential nomination at the outset of the convention. Seward's detractors believed that his well-publicized reference to a "higher law" than those protecting slavery and to the "irrepressible conflict" between slaveholding and free societies rendered his candidacy controversial enough to endanger their own prospects of election should he head the Republican ticket. Hence they sought a more "available" (less well-known) nominee. The result of these machinations was the choice of Abraham Lincoln as the Republican presidential candidate and a commitment by Lincoln's floor managers to propose Cameron for a Cabinet position, while Cameron was to assist Curtin's election in October. All went as planned: Lincoln won the presidency, Cameron became his secretary of war, and Curtin was sworn in as governor of Pennsylvania, serving in that office from 15 January 1861 until 15 January 1867.