The Know Nothing Party won seats by declaring Catholics inassimilable

Evidence

The more politically influential American Party, also known as the Know Nothing Party, was among the most vocal denouncers of Catholics. The Know Nothing Party declared Catholics inassimilable, perpetuating rumors that Catholics were unfit for self-government on account of their blind loyalty to the pope. The anti-Catholic fervor won the Know Nothing candidates seats in local and state office in Massachusetts, New York, and other northeastern states in the 1854 elections. — Sahar F. Aziz, The Racial Muslim, 308

Categorization

• XREF: The ‘inassimilable’ framing is the exact word later applied to Muslims — the same declension of ‘unfitness for self-government’ recycled across centuries and targets.