The Beltway wisdom is that moderate Mitt Romney is the most marketable candidate to non-Republicans and therefore the most electable candidate in the GOP field. Rick Santorum, on the other hand, is widely viewed as too conservative on social issues to appeal broadly to American voters. Even though Mr. Santorum has won more states than anyone in the Republican primary and caucus process, his wins have been written off as special situations where evangelical Christians enjoy outsized influence.
Let me see if I can translate into “flyover” country language; “The Beltway wisdom” = people who live and work for the government in Washington DC who also live inside a bubble that bears little resemblance to actual life in America. “the most marketable candidate to non-Republicans” means “the person the sane voters can accept without throwing up. And “too conservative on social issues to appeal broadly to American voters” comes over as “the views some people who actually read the Constitution and know exactly what principles the country was founded on – those OTHER voters (and WHY do we even bother LETTING those yahoos have a vote in the first place??) that no one likes to pay attention to.