Good article sums up the night in Wisconsin.
Exit Polls: Why Obama Won
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Obama chalked up his ninth straight victory and won in this predominantly white state with a strong showing across a broad spectrum of voters and by eating into Hillary Clinton's base of support. He nearly tied her among women, won on all of the issues and won every income level. He also won the white vote under-60."
...."
Electability has been something both campaigns have been touting. Tonight, Obama beat Clinton soundly -- 63%- 37% -- when voters were asked who would be most likely to beat the Republican candidate in the fall.
One other note regarding the negative attacks this past week: Wisconsin Democrats took notice.
When we asked if either of these candidates attacked the other unfairly, 53% said that Clinton was unfair, while only 33% said the same about Obama.
Not all is lost, however, for Clinton. She still took the senior vote, those with less than a college education and Catholics, but it was not enough to overtake Obama."
http://firstread.msnbc.msn.com/archive/2008/02/19/683081.aspx