A savvy reader emails:
I haven't seen all the exit data, but listening to the talking heads it seems Obama is finally cracking the code of the working class white voter. But maybe it is simpler than that.
Could it be that downscale voters are also "low-information" voters when compared with their Volvo-driving broadband-surfing upscale brethren? If so, it would suggest that all it was going to take was a bit of time for the word to get through that Obama is looking like a winner. Wealthier voters may be the leading edge of a wave. Downscale voters may be the ones who catch trends later--and then really give them mass market power. If so, it's bad news for Senator Clinton going into Ohio and Pennsylvania.
Sounds plausible to me. Indeed the post-Iowa mass shift of black voters to Obama, though more complicated for racial reasons, may have partly reflected this phenomenon in miniature: For months black voters had a vague sense that Obama couldn't win. But once it was clear that he could, they flocked to support him.