This is not pumping up how religious they were during elections, but Plutarch seems to think politicians did have to appeal to the superstitious nature of the population.

I'm reading On the Sign of Socrates (from Moralia Frank Cole Babbitt translation) for my own research. Here's what Plutarch puts into Galaxidorus' mouth:

"How hard is it to find a man untainted with humbug and superstition! Some, through no desire of their own, succumb to these disorders from ignorance or weakness, whereas others, to be reputed the favourites of heaven and above the common sort, invest their doings with a character of sanctity, hiding what occurs to their intelligence behind a pretence of dreams and apparitions and the like mummery. For men engaged in public affairs and compelled to live at the caprice of a self-willed and licentious mob this may have its use-to treat the superstition of the populace as a bridle, and thereby pull them back to the profitable course and set them right;"

This question assumes that any modern politician who is seen to be religious must be pretending in order to appeal to the masses, and that genuine religious feeling cannot be present in any modern politician.