Publicly, Democrats are projecting great confidence about the likelihood of taking back the Wisconsin state senate in the upcoming recall elections. They claim their private polling shows them ahead or tied in all six races targeting GOPers for recall, while the two Dems being targeted seem safe. Beltway observers like Stuart Rothenberg are confident Dems are on track to win.

In reality, Democrats know full well their bid to take back the state senate could still fail.

Here’s why. While it’s become a tedious cliche to point out that in the end elections all come down to turnout, in the case of the Wisconsin recall elections it really will prove decisive.

And what’s got Dems particularly nervous is that in these races, there’s no precedent for predicting what turnout is going to look like — because we’ve never before seen anything like this set of recall elections.

“We don’t have a precedent for this,” Mark Mellman, the well respected Dem pollster who is conducting recall polling for the Wisconsin Democratic Party, acknowledged to me. “The nature of the turnout is so uncertain that it really will make a huge difference. We’re dealing with big uncertainties.”

Mellman said that three of the key races — though he wouldn’t specify which — are so close that if turnout doesn’t break the Dems’ way, it could throw them to Republicans. He described them as “all very close races that could go either way.”

Dems think they’re very likely to oust senator Dan Kapanke, and are somewhat confident that they will defeat Randy Hopper. Dems need to net three wins to take back the state senate, so they are eyeing either Luther Olsen or Alberta Darling as the potential third victory. Sheila Harsdorf is also possible.

One factor potentially working against Democrats is that Republicans tend to turn out more in traditionally low-turnout elections, as Mellman noted. The recalls are off year elections, so you’d think they’d be low turnout. But Scott Walker’s proposals have produced a backlash and level of grassroots energy that caught the most seasoned observers off guard.

“We believe that the tremendous antipathy that Walker has engendered will mean a significant Democratic turnout,” Mellman said. “But there’s no way of knowing whether it will happen.”

The question is whether the anti-Walker energy has dissipated in recent weeks. Union activists are taking no chances, and have built up a turnout operation they believe is superior to that of the GOP. Meanwhile, in a potential good sign for Dems, Republicans are conceding that the energy is on the Dems’ side. As one GOP operative involved in the recall fight puts it: “The average Republican voters in Wisconsin viewed the passage of the Walker proposals in March as the end of a tough battle, while Democrats viewed it as the beginning.”

That’s true. But for now, there’s no predicting whether it will be enough.