Speculation about disgruntled Clinton Democrats defecting to McCain has been one of the subtexts of this very long primary season. I don’t buy it. I think Obama will eventually unify the self-identified Democrats and score big margins among these partisans in November. Independents may be a different story, but defections among self-identified Democrats have been at 10% or less in every presidential election since 1992, according to data from the American National Election Study at the University of Michigan. I see no reason why that pattern won’t continue. This Gallup poll released today supports that conclusion. It shows Obama beginning to improve among constituencies where he previously struggled–women, less well-educated voters, and whites. According to Gallup: