Why did Protestant Americans believe that Roman Catholics could never be loyal Americans?

Protestant Americans often believed that Roman Catholics could never be loyal Americans due to concerns about divided loyalties, fearing that Catholics would prioritize their allegiance to the Pope and the Catholic Church over their commitment to the United States. This perception was fueled by historical tensions, religious differences, and anti-Catholic sentiment, particularly during periods of Immigration when large numbers of Catholics arrived in the U.S. Additionally, Protestant leaders sometimes portrayed Catholicism as a threat to American values and democracy, further entrenching these beliefs among Protestant communities.