What adds another twist to the politics is that Mitt Romney not only endorsed Mourdock but cut an ad for him that started running in the state earlier this week. To the best of my knowledge, Romney hasn't done that for any other Senate candidate in the country.
Last night the Romney campaign put out a statement disagreeing with Mourdock's comment but not denouncing him. And the campaign did not respond to questions about whether he was withdrawing his endorsement.
The key though is the ad. Democrats are pushing hard for him to ask Mourdock to take it down. And if the Mourdock story grows, I suspect he'll have to ask him to take it down, which would be devastating for Mourdock -- not so much because of the ad not showing but because fo the merciless press it could spawn so close to election day.
The fate of the ad is what I'd watch to see where this story is going over the course of the day.
Late Update: The Romney campaign has now said they have not asked Mourdock to take down the ad.
Later Update: Freshman GOP Sen. Kelly Ayotte cancels trip to campaign with Mourdock.
Even Later Update: Romney reaffirms support for Mourdock candidacy.