There's a problem with Rasmussen's party id percentages. He weights his poll according to national averages and as a result samples a lot more democrats than republicans. But from what I heard on the radio this am he may want to adjust his sampling. There's a poll out this week...can't tell you which...that has party id among those who claim a party affiliation at 48% dem and 47% GOP. They claim they've seem a huge swing since the GOP convention.
Rasmussen said that if there was a sudden swing in party affiliation percentages that his polling would be way off until he caught the swing.