There are conservatives who could do it without crossing the line -- but too many who'd stir controversy by going over it.
My colleague David Graham is right that there is no compelling moral reason that Jeremiah Wright should be off limits in the upcoming presidential campaign. But I think Mitt Romney is smart to distance himself from any attacks that invoke the controversial pastor, as was John McCain. It isn't that any attack mentioning Rev. Wright is racist. Or that anyone who attacked would come off that way. But let's not be naive about the partisans Team Red is working with. There are a not insignificant number of Republican boosters and conservative movement figures who just can't be trusted to talk about racially fraught controversies in a way that isn't going to embarrass or reflect poorly on the right, starting with guys like Rush Limbaugh, who have an incentive to piss people off in attention grabbing ways, and running all the way down to some state or county Republican Party staffer who finds racially offensive emails funny enough to forward.
Although hard core conservatives can't see it, President Obama is adept at talking about race in America. He's thought about the issue long enough to speak about it with simple words and sophisticated nuance. He invokes the best of America when telling the story of his life. He can tell a story about why he attended that church that makes white people listening feel good about their country and themselves. Mitt Romney cannot talk about race like that, nor does he benefit from an inquisition into how he could participate in his own faith given its flaws over the last five decades.