Actually, per the exit polls, the Republican rank and file like Romney just fine

Yes, his home state of Michigan was closer than Romney expected it would be a month ago (although not two weeks ago, when one poll had Rick Santorum winning there by 12 points). But the key detail in the exit polling from Michigan was this: Romney won the votes of self-described Republicans by 10 points, 47 percent to 37 percent.

The fact that Romney didn’t win by a landslide in Michigan was apparently the result, in whole or in part, of mischievous Democratic voters trying to weaken him. Exit polls suggest that those voters added as much as 3.5 percentage points to Santorum’s total.

Santorum slaughtered Romney among those Michigan voters who said they wanted a “true conservative,” by a margin of 57-17. But those voters made up only 12 percent of the electorate.

Most of the commentary you read and hear about the GOP — especially from the Right itself — would lead you to think those highly ideological voters constitute a near-majority. The truth is more complicated.