It would be because of their bigotry that Catholics
Is this not largely a self-selection process? Some notable conservative GOP luminaries like Boehner are reputed to be faithful Roman Catholics. Why hasn’t Boehner even made noises about it?
In 1964 I was proud to vote for William Miller, the Catholic running mate for VP on the GOP ticket with Barry Goldwater. As an Evangelical Christian, it never occurred to me to vote for or against him because of his religion.