Some say Mormons aren't Protestant. Some say Obama is a closet atheist. So 2012 OTL of one agrees with either of those views, since Biden and Ryan are Catholic.
I'll accept Mormons as non-Protestants because of the way they're viewed by the rest of the US sure, Obama being a secret atheist is unprovable so I'd say no, lol

, despite agreeing with your broader point of politicians pretending to be religious because well, America.
Well, OTL you have the 2012 Republican ticket of Mitt Romney (Mormon) and Paul Ryan (Catholic).
You're right, my bad on not being clearer

. Let's say earliest/most plausible before then.
I think the earliest time would be the 1990s
I could very easily see a Catholic-Catholic ticket starting in the '90s though. Jerry Brown / Mario Cuomo for example. Gingrich / Ryan.
I doubt Cuomo would take VP under anybody (he specifically told Clinton to rule him out IOTL), but sure double Catholics in the 1990s seems the most likely. But let's flex our collective US political knowledge. Perhaps Ben Nighthorse Campbell works re: my Native American thought bubble if he adopts his father's religion instead of his mother's?