Take a look at the outcome in MI, GA, and tell me they weren't overwhelmingly won. I do agree with you that the margins keep shrinking.
That's why I suggested that social conservatives ought to focus on separating marriage and state while they still have enough leverage to do so. (On another topic, national security conservatives ought to focus on extricating the US from Barack's Bogus Libyan Adventure before it becomes a bigger mess than it is already. The logic is similar -- all it takes is getting past the irrational hang-up that going for the best achievable objective is some sort of "surrender".)