The first time I have ever heard about “magic underwear” was whe it was used to belittle Romney on this site. It has since been repeated countless times. Romney’s Mormonism has been cited to countless times.
I’ve kidded about it too. I said it’s fine with me if Mitt manages to strangle Obama with some magic long johns.
We’re talking about a space case religion. How that influences Mitt is far less clear to me, but it might be clearer to others. There is an official clean living side to the LDS, and then there is a libertine undercurrent (hardly anyone outside the LDS thinks Joseph Smith was just a disinterested prophet, even if mistaken about what he was channeling).