The most appropriate conclusion that could be drawn from the fact that Millard Fillmore was the Know-Nothing candidate in the election of 1856 and received 21 percent of the popular vote is:
- A significant number of people were hostile toward immigrants.
The Know-Nothing Party, also known as the American Party, was primarily focused on anti-immigrant and anti-Catholic sentiments, reflecting a broader nativist attitude in the mid-19th century United States.