Structural Causes of the "Enthusiasm Gap"
In analyses of the current political climate, an awful lot of stock has been placed in the so-called "enthusiasm gap" between Republicans and Democrats. Sometimes this "gap" is based on polling that actually asks voters about their level of enthusiasm towards voting this year. The problem with such measurements, of course, is that "very enthusiastic" voters don't get an extra vote; the key variable is willingness to vote, not the degree of passion with which a vote is cast.
More often than not, though, the "enthusiasm gap" has become synonymous with the more meaningful idea that Republicans will have a turnout advantage in November. And while this probability is frequently identified with a relative level of unhappiness among Democrats for the Obama administration and/or congressional Democrats, it cannot be repeated too often that midterm turnout is invariably higher among older and whiter voters. And it just so happens that the Democratic support base as of 2008 was unusually correlated with the youth and diversity of voters.
That's true today as well. Looking at Gallup's latest presidential job approval tracking poll, Obama's positive ratings remain inversely correlated with age, and thus with the proclivity to vote in midterms, ranging from 56% among 18-29 year-olds; to 38% among over-65s. His approval rating among nonwhite voters, another traditionally underperforming demographic group in midterms, is 65% (among African-Americans, it's 90%).
Meanwhile, 78% of Democrats and 73% of self-identified "liberals" approve of the President's job performance. These are not optimal numbers, but nor do they suggest a deep malaise. At this point in his presidency, 70% of Democrats approved of Bill Clinton's job performance, and he went on to win re-election handily. And since it's de rigour to compare Obama to Jimmy Carter these days, it's worth noting the 52% job approval rating among Democrats for Jimmy Carter at this point in his presidency (Carter's Democratic approval rating eventually bottomed out in the autumn of 1979 at 40%).
None of this provides any Democratic comfort for the midterms themselves, but it should be reasonably clear that structural factors account for much of the "enthusiasm gap." And the minute the 2012 presidential cycle begins, the same factors will create a much more positive environment for Obama, even if you don't consider the unimpressive Republican presidential field.