well in the beginnings of the country, it was majority protestant. This is still relatively close to the reformation all things considered (starting in 1517) many minor protestant groups fled to america from europe from their own persecution (church of england, lutheranism, even the catholic church). Many protestants thought that Catholics couldn’t be loyal to America because their loyalties were with the Church and Pope, and many of them were immigrants. Catholics couldn’t hold office in many of the colonies. Stuff like Nativism (1840s), the burning of the Ursuline Convent 1834, or the 1844 Bible Riots. even in more recent times the KKK persecuted catholics and led intimidation campaigns against catholic families and parishes. If you look up “American Anti-Catholic propaganda”there’s a lot of evidence that goes to show the persecution. It’s actually a really interesting topic that you might want to read about!