It’s been a tough year for Obama’s liberal base.  The Democrats lost the House and Harry Reid lost his ability to shape the narrative, which means that legislative fights will be fought on Republican terms, especially on spending.  Thanks to our new adventure in Libya, the anti-war crowd has little to cheer, too.  That likely explains why Barack Obama has hit a new low for strong approval among self-described liberals in the Rasmussen tracking poll:

The Rasmussen Reports daily Presidential Tracking Poll for Monday shows that 19% of the nation’s voters Strongly Approve of the way that Barack Obama is performing his role as president. Thirty-nine percent (39%) Strongly Disapprove, giving Obama a Presidential Approval Index rating of -20 (see trends).

Today’s numbers reflect the lowest level of Strong Approval yet recorded for this president. There has been a sharp decline in enthusiasm among liberal voters.

Currently, just 37% of liberals Strongly Approve of the president’s performance. That’s down from 63% a year ago, 57% at the beginning of 2011, and 52% a week ago. Some liberal commentators have expressed disappointment with the president over the extension of the Bush tax cuts, the military action in Libya, and, most recently, the budget deal to avert a partial shutdown of the federal government. While liberal enthusiasm may be declining, 57% of voters believe thepresident is more liberal than they are.

Overall, Obama’s approval numbers haven’t changed much, at 44/55.  The impact on liberals hasn’t tilted them into disapproval — at least not yet.  Obama gets an 84% approval rating with liberals and 54% with moderates, but the enthusiasm is dissipating from his base, which is a bad way to start a re-election campaign.

Still, these are not numbers that guarantee a loss in 2012.  The base may be unenthusiastic, but they will have nowhere else to go in a 2012 general election.  If their disaffection starts bringing down Obama’s approval numbers in a serious way, it could provide a signal for a primary challenge in the fall from a Democrat more aligned with the anti-war Left, perhaps especially if the GOP forces Obama to start proposing significant cuts to entitlements.  These numbers make that a remote possibility, though, and there isn’t any significant national figure among Democrats who could run to Obama’s left — certainly not Hillary Clinton, who ran to his right in 2008 and is most responsible for the decision to start a war in Libya that isn’t going terribly well now.  Bill Richardson may be the only non-fringe candidate on the scene with enough credibility to make Obama sweat, or perhaps Russ Feingold, who would be much less inclined to try it.

Obama won’t worry that the liberals will defect to the GOP, or that they’ll prompt a legitimate third-party general election run on the Left.  His big worry is that they just won’t show up, either at the voting booth or as volunteers to raise funds and conduct GOTV efforts.  That would make the difference in what already looks like a difficult election cycle for Democrats, and might hurt Democrats running for the Senate and House more than Obama himself.