The Democrats had 10 million new voters in 2008, and they won by 10 million votes. Their perception is their new voters voted early.
The Democrat belief is that Republicans have fewer new voters, and they tend to vote on election day with only a handful of absentee ballots earlier.
When the Democrats see their early voters NOT VOTING and the Republicans having a whole huge bunch of presumably new voters voting early, they assume ~ correctly ~ they are losing.
So, how did this come about ~ well, rather than deal with a Republican governor regarding government employee pensions democrats ran away ~ literally ~ and hid out in Illinois. More than likely this sent a message to their new voters that Democrat politics in Wisconsin extends no further than government employee benefits and retirement packages.
Since so many of the new voters were youth, and have spent the next 4 years unemployed, it's not all that likely they are real excited about voting for Democrats.
Consider yourself *highly* recommended.
Cheers!