The most interesting question not being asked by social conservatives and MSNBC liberals is: Why isn’t Rick Santorum catching on? According to both groups, Santorum should be doing better. We all have theories about why Romney can’t close the deal. But no one has really explained why Santorum can’t close the deal. Liberals think the GOP is hard-core conservative (albeit with more pejorative labels), but the hard-core conservative in the race isn’t taking off. Social conservatives say that evangelicals care about Santorum’s issues. He was even endorsed by evangelical leaders recently. But it’s not working. Why?