When he’s not talking about Venezuela or Iran, Rick Santorum can be pretty sensible (via Sullivan):

And then on the issue of, on social conservative issues, you point to me one time John McCain every took the floor of the United States Senate to talk about a social conservative issue. It never happened. I mean, this is a guy who says he believes in these things, but I can tell you, inside the room, when we were in these meetings, there was nobody who fought harder not to have these votes before the United States Senate on some of the most important social conservative issues, whether it’s marriage or abortion or the like. He always fought against us to even bring them up, because he was uncomfortable voting for them. So I mean, this is just not a guy I think in the end that washes with the mainstream of the Republican Party. 

That sums it up pretty well.  Meanwhile, you supposedly three other leading candidates, one of whom has no real credibility on social issues, one of whom is effectively on the other side of the debate and the third who is evidently entirely reliable.  Social and cultural conservatives make up a much larger part of the party than do economic conservatives, and three of the four leading candidates are essentially unacceptable to large numbers of them for different reasons.  All other things being equal, if you wanted to choose the candidate who had the best chance of turning these voters out in November and keeping as much of the coalition together as possible, wouldn’t you choose the one who can most reliably motivate your largest voting bloc?  Are economic and “national security” conservatives really going to sit out a Huckabee-Clinton or Huckabee-Obama election?  It’s not as if they are likely to vote for the other party!  (Bush Hawks for Obama does have an amusing ring to it, but I don’t think we’re going to see it this year.)  As they have said to social conservatives so many times before: where are you going to go?