John M. Murrin, et al., eds., Liberty Equality Power: A History of the American People, 2nd ed., vol. 1 (Fort Worth: Harcourt Brace, 1999), 476-477.
This would be a three-party election, for the American Party was still in the field, despite the exodus of most of its northern members to the Republicans. Having become mainly a way station for former southern Whigs, the party nominate ex-Whig Millard Fillmore. The three-party campaign sifts out into a pair of two-party contests: Democrats versus Americans in the South; Democrats versus Republicans in the North. Fillmore, despite a good showing of 44 percent of the popular vote in the South, carried only the single slave state of Maryland. Considering Buchanan colorless but safe, the rest of the South gave him three-fourths of the electoral votes he needed for victory...Buchanan needed only to carry Pennsylvania and either Indiana or Illinois to win the presidency, and the campaign focused on those states. The immigrant and working-class voters of the eastern cities and the rural voters of the lower Midwest, descendants of upland southerners who had settled there, were antiblack and antiabolitionist in sentiment. They were ripe for Democratic propaganda that accused Republicans of favoring racial equality.