After going Republican for several election cycles from 1968 to 1988, Michigan moved to the Democratic column in presidential elections from 1992 to 2004. While Bill Clinton carried the state quite comfortably in his two elections, Al Gore and John Kerry carried them by much smaller margins: Gore by 217,279 votes, Kerry by 165,437.
That said, with 100,000 DEMOCRATS making the special trip out to vote for NO ONE over Hillary Clinton, it's hard to see how she wins this "must have" state in a general election. To those 100,000 voters, add independent and Democratic voters who didn't cast a ballot in yesterday's primary but who will vote in November, and the math just doesn't look good for Sen. Clinton.
And if you can figure out how she wins the Electoral College without Michigan's 18 votes, I'd love to hear it.