Two days ago, I floated a theory about the awful string of special elections this spring. The specials in IL-14, LA-6, and MS-1 all followed Democratic primaries in those states, while the Democratic nominating contest was going on. Meanwhile, special elections in OH-5, MA-5, and IN-7, ending in mid-February, yielded results well within expectations with slight boomlets for the Republican candidates. All of these primaries occurred well before Democrats had been primed to vote in the Presidential primary in those states.
This theory is bolstered by this chart posted on Open Left a month back: