D+12......how far can you go??? rofl
So the random sample of respondents had 12% more people identifying as Democrats. This seems more likely to indicate that more people are identifying as Democrats than that the sample is skewed. Party ID is something that can easily change; personally speaking, in 37 years as a voter I've identified at various times as a Republican, a Democrat, a Libertarian, and most recently as an Independent.
If only one or two of these polls showed "unexpectedly" large D samples, it would probably mean they were outlying samples. But when a LOT of polls -- from multiple pollsters -- show such samples...it's probably a better indication that the electorate's self-identification is changing.
