Why was Jennifer Granholm re-elected by such a wide margin in 2006?

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Michigan was a pretty blue state until the last few years, in 2004 it was 6% more democratic, than the nation, 2006 was a D+8 year so Granholm winning by 14% is what you would expect.

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One thing I would note is a lot of Midwestern  states like MI, WI, IA, all stayed the same relative to the popular vote between 2004 and 2012. MI had a D+6 lean in 2004 and D+5.6 in 2012, WI had a D+2.9 lean in 2004 and D+3 in 2012, IA had a D+1.8 lean in 2004 and D+1.9 in 2012.

The only one of the big states in the north that had any Republican trend from 2004-2012 was PA that went from D+4.5 in 2004 to D+3 in 2008 to D+1.5 in 2012 in terms of its lean and that was due to it having parts of Appalachia which caused it to trend R in 2004-2008 in direct contrast to most other northern swing states that trended democratic.