Nothing to do with him being Catholic. It’s how he lived his debauched life, Old Joe buying his Senate election which was common knowledge, etc. Those aren’t Christian characteristics.
“Wherefore by their fruits ye shall know them.” Matthew 7:20
Also ... Democrat. There’s that.
Saying they were Christian and Republican implied to me they were both factors in determing the vote. It followed that they saw JFK as un-Christian. I don’t remember how much ‘debauchment’ was known before the election. Didn’t that all come out later?
I think the only reason, which is reason enough, they voted for Nixon was because Tricky Dick was a Republican. My folks voted Democrat regardless, too.