Millard Fillmore took presidency after Zachary Taylor died, only having been in office for a little over a year. Fillmore is considered one of the worst because he supported the Compromise of 1850- which included the Fugitive Slave Act. The Fugitive Slave Act compelled the government to return runaway slaves to their masters, which stood for everything that Zachary Taylor opposed (Tolson). Fillmore’s hopes in doing this was delaying the South’s secession from the Union, which it did, but only for awhile.
Tolson , Jay. “Worst Presidents: Millard Fillmore (1850-1853).” U.S. News & World Report, U.S. News & World Report, 16 Feb. 2007, http://www.usnews.com/news/special-reports/the-worst-presidents/articles/2014/12/17/worst-presidents-millard-fillmore-1850-1853.