I read an editorial a few days ago suggesting a reason the MSM and the White House want to run against Romney - and it has everything to do with playing the race card. While people of African descent have always been able to be members of the LDS, it was only as recently as 1978 that the Church permitted them to enter the priesthood.
Read this link..... while I don't think Obama's people would directly call Romney a racist, by attacking his religion and it's history with black Americans, the inference that he's a racist would be very easy, particularly since few know the history of LDS and it's teachings.
Having said that, it certainly didn't matter about Obama's 20-year involvement with an anti-American pastor, but then - McCain was unwilling to attack Obama on his associations. The left WOULD NOT HESITATE to attack Romney, even indirectly, for his associations.