One name mentioned is Tom Barrett, the mayor of Milwaukee who ran against Walker in 2010. Tim Cullen, a state senator, has said he is running. Former Dane County executive Kathleen Falk and former Rep. Dave Obey, among others, are names that are also tossed around.
No clear Democratic contender could potentially mean a contested primary, forcing candidates to expend resources in advance of the general election.
At the same time, it's important to underscore that it is early, and the focus on the Democratic side right now is on collecting signatures. There is time for the party to coalesce around one candidate -- it's just not yet clear who that person is.
Laying The Groundwork: Walker has been running TV ads, staffing up with experienced hands and raising money. He's not simply sitting back and waiting to see if a recall will be triggered. His operation is moving ahead with the expectation that an election will take place.
Right now, he's not competing over the airwaves with anyone, so whoever the Democratic nominee is will have to play a bit of catch up.
Recent History: Democrats picked up two state Senate seats in the summer recalls, but ultimately fell just short of the coveted prize: seizing control of the state Senate. That left a lot of activists and labor organizers disappointed. It's difficult to gauge what the energy level will be statewide in 2012, but it's not clear from the results of the summer that Walker is toast just yet.