GG - I've come to suspect it's the caucus system.
Iowa spun out two wing-nuts, one for the Republicans and one for the Dems. The Reps. managed to sideline their wing-nut, but not without losing Romney. The Dems seem destined to stick themselves with their's, just like then did with Kerry in 2004.

                  When you look at the results of later caucuses, the pattern becomes more obvious. It wounds the Dems. worse than it wounds the Reps.