Jean H. Baker, "Blair, Montgomery," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00112.html.
Blair, along with his influential brother Francis Blair and his father [Francis Preston Blair], had come to oppose slavery and to support the return of freed blacks to Africa, the latter a policy that he believed would encourage southerners to free their slaves. Blair's views on slavery were representative of a body of border-state opinion, which opposed abolitionism and black equality as too extreme but which argued for a containment of slavery and its gradual end. In 1848 he was associated with the Free Soil party, attracted to that new organization during a period of party realignment by friends in New York. By 1852 he had returned to the Democratic party and was a delegate to its national convention. By 1860 he supported the Republican party and worked hard, though largely unsuccessfully, to organize this new political organization in Maryland.