He trails his Republican challenger, Ron Johnson, by double-digits in the latest Public Policy Polling survey. Why is that shocking? Feingold is a multi-term incumbent and hard-left liberal who was expected to sail to a relatively smooth reelection. Now he’s on the path to a rough defeat.

Ron Johnson (R) 52 (43)
Sen. Russ Feingold (D) 41 (45)

An enormous enthusiasm gap, coupled with a Republican nominee fresh from a decisive primary win and unsullied by the primary process, has catapulted Republican nominee Ron Johnson to a double-digit advantage over incumbent Democrat Russ Feingold, according to PPP’s poll of the state on behalf of Daily Kos.

In November of 2008, then-candidate Barack Obama swept through the Midwest, winning many states (including Wisconsin) by double digits. Today, the President’s numbers are nearly reversed in the Badger State: whereas Obama carried the state 56-42 in 2008, his job approval now is 41%, with 54% expressing disapproval. This is a tendency that has been mimicked throughout the Midwest, and may well explain why this region seems to be the one vexing Democrats the most this cycle.

In case you didn’t bother to read that second paragraph (I’m often guilty of skimming myself), Obama carried the state of Wisconsin by double-digits — the same margin by which Feingold is now trailing. The state hasn’t given a Republican presidential nominee its electoral votes since Reagan in ’84.

The outlook is gloomy for Democrats. Even if they were capable of driving the same number of party members to the polls in 2010 as they did in 2008 — highly improbable to say the least — the race would still be within a point. Democrats could excite their activists, get all of Obama’s voters back to the polls, and still face defeat.