What effect would being an ex-Mormon have on a Presidential campaign?

[I spent the winter writing songs about getting better]

It's unclear if Romney's Mormonism is a net plus or negative or no effect (clearly at least a small net negative electorally but a large plus in fundraising), but how would a candidate raised LDS but who abandoned it fare and what would the effect be? Let's assume that they renounced Mormonism and converted to something very generic and inoffensive to both sides (Methodist is a good denomination to use as an example.) Keep in mind renouncing Mormonism and excommunication is treated pretty seriously by the LDS church which even holds sort of "trials" over the sort of thing, it's not as simple as simply requesting they take your name off any type of membership.

For a Democrat, it'd probably be entirely moot, though if the primary was competitive until Utah that might be an interesting state to look at but I doubt the people who are Democrats in Utah overall have much fondness for the LDS (even amongst those who are nominal members and simply don't practice rather than go through the formal renouncement) and if things got as heated as 2008 some forums like DU would have idiot hacks of the other candidate coming up with crazy Manchurian candidate type theories or "proof" they did not leave the LDS and are probably trying to fulfill the White Horse Prophecy, but no one remotely mainstream would pay any attention to it and it would be an effective non-issue. They might get destroyed even worse than an average Democrat in Utah in the general but not an issue of concern.

For a Republican, eh well it depends on what type of candidate they are. For a staunch conservative, it'd probably be a wash, evangelicals would like it, but the Mormon vote might be pretty strongly against them unless they were the only solid conservative. For a wishy-washy sort of moderate like Huntsman (he'd actually be the best example even if he wasn't Mormon), then they wouldn't get the Mormon vote anyway, but they also aren't winning the nomination. And for someone who constantly flips around and is as chameleon-esque as Romney, they'd probably perform similar to Romney except they obviously wouldn't win the Mormon vote (and might not be as well funded either of course which makes a big difference.)