Fillmore 's allies were in full control of the American Party , and they arranged for him to get its presidential nomination while he was in Europe . The Know Nothing convention chose Andrew Jackson Donelson of Kentucky to be Fillmore 's running mate ; he was the nephew by marriage and onetime ward of President Jackson . Fillmore made a celebrated return in June 1856 , speaking at a series of welcomes , which began with his arrival at a huge reception in New York City and continued across the state to Buffalo . These addresses were portrayed as expressions of thanks for his reception , rather than as campaign speeches , which might be considered illicit office-seeking if made by a presidential hopeful . Fillmore warned that electing the Republican candidate , former California senator John C. Frémont , who had no support in the South , would divide the Union and lead to civil war . Both Fillmore and the Democratic candidate , former Pennsylvania senator James Buchanan , agreed that slavery was principally a matter for state and not federal government . Fillmore rarely spoke about the immigration question , and focused on the sectional divide , urging preservation of the Union
Know Nothing convention
1856 American National Convention
Millard Fillmore