The most accurate conclusion that can be drawn from the fact that Millard Fillmore received 21 percent of the popular vote as the Know-Nothing candidate in the election of 1856 is:
A significant number of people were hostile toward immigrants.
The Know-Nothing Party, also known as the American Party, primarily focused on nativism and had a strong anti-immigrant agenda, especially against Irish and German immigrants. Their platform emphasized the need to limit the influence of immigrants in politics and society.