Charles M. Hubbard, "Mason, James Murray," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00666.html.
Unlike most political leaders from the Upper South, Mason strongly believed that slaveholders' rights could not be protected within the Union and supported the radical secessionist leadership of the South. In Mason's view, the industrializing North, corrupted by banking interests, threatened the southern way of life. A strict constructionist, he was the author of the Fugitive Slave Law of 1850 and believed slavery should be expanded into the territories without restrictions. In 1850 he refused to join Robert Toombs, Howell Cobb, William L. Yancey, and other southern moderates and instead allied himself with Robert Barnwell Rhett and other obstructionists, who refused any concessions to the antislavery element in Congress in the interest of a compromise on the issue of slavery in the territories. By that time Mason did not wish to preserve a Union that rejected southern values and leadership, and he was prepared to secede from the Union. In 1856 he was similarly outspoken in his commitment to lead Virginia out of the Union if the newly formed Republican party was successful in electing John C. Frémont as president.