This is not to suggest that the pattern will necessarily be the same in 2012. In contrast to this year — when Mr. Obama ultimately had much to show off to liberals, including a health care bill and a financial regulation package — it is difficult to see how any major liberal priories will be advanced once Republicans take over the House in January. But Democrats could still pass some proposals popular with liberals, like the reversal of the military’s “don’t ask, don’t tell” policy, before the 111th Congress concludes its business later this month.

Still, just because liberals are disappointed with Mr. Obama does not necessarily mean they will fail to turn out and vote for him when the only other choice is a Republican. In some ways, it probably helps Mr. Obama that the country has become so polarized and that liberals view Republicans as such an unacceptable alternative, and vice versa. The prospect of a President Palin or a President Gingrich would surely motivate most liberals to vote — and even comparatively moderate Republican candidates like Mitt Romney will be under pressure to show their conservative stripes during the l Republican primaries and are likely to campaign on policies, like a repeal of the health care bill, that liberals overwhelmingly object to.