I noted earlier tonight, as the Michigan returns were coming in, that Mitt Romney’s lead in Michigan was due in large part to his strong margins in the five-county metro Detroit area, where Republican voters tend to be relatively upscale—not all rich people from Bloomfield Hills, Romney’s boyhood home, but from the relatively comfortable and competent suburbs in a metro area that has been troubled. The returns at this writing show that almost all of Romney’s statewide margin came from Oakland County, the relatively affluent suburban county just northwest of Detroit, which is the state’s second largest county and the one that cast the most votes in the Republican primary.

Four years ago Romney carried the five-county metro Detroit area 45%-27% over John McCain; this time he carried it 45%-32% against Rick Santorum. His metro Detroit margin enabled him four years ago to convert a narrow Outstate 35%-32% margin to a convincing 39%-30% victory. His metro Detroit margin this time was enough to overcome a 42%-38% Santorum margin Outstate.