At least if the GOP establishment has their way. He was their favorite to begin with because he's really a big business guy but he pretends to have "traditional values." Just like Reagan and the Bushes. The GOP doesn't want an actual social conservative as the President, just one that can talk the talk during an election but then sell out the middle class to the highest bidder once they get into office.
Notice how when they got an actual social conservative in the running (Huckabee) most of the conservatives in the media were against him. It's because all this value stuff they talk about is just bulls**t. Thomas Frank explained it best in "What's the Matter with Kansas." They are content to get the votes of the social conservatives in the Southeast and Midwest but don't want them to actually govern because that wouldn't do anything to help big business.
Since McCain was so reluctant to release his medical records, and when he did it was for a limited group of people for only 3 hours and being over 1000 pages in length, they never really got through all of it...I think there must be some medical condition he has that is likely to cause him to not make it through his first term as President.
Since the leaders of the GOP know this, they have to think about who they want to take over when McCain is out of office. They don't like McCain, but they are willingly to use him as a Trojan Horse to get Romney into office, who will do everything they say.
Ironically, they would really have a chance of winning if Huckabee was VP. Not only is he attractive to social conservatives but he'd also pull in the Libertarians with his Fair Tax ideas. But he's not one of them, they wouldn't be able to control him and he might do things that they don't like (even though he'd be true to the principles they pretend to believe in).
They definitely don't want Liebermann or anyone else pro-choice. They've done an amazing job keeping their base of middle class social conservatives despite hurting these people economically to the point of collapse. There is no way the GOP leadership wants to risk a good chunk of their base to suddenly stop voting on social issues and instead voting for their own economic well-being.
The day that happens, and it will, the Republican Party as we know it becomes extinct.
Update: On the topic of Romney being a Mormon: The leaders of the GOP aren't really religious, they just pretend to be. Because of that I don't think they understand the issue of the evangelicals being afraid of Romney's religion. Does he talk about God a lot? Okay, that works. To them religion is religion, whatever, as long as he can make them lots of money. The GOP is controlled by the super rich that don't have much contact with regular people and have no clue what the "peasants" really think.