Here's an answer:
n a year in which Democrats have a lead of 11 million registered-voters over Republicans, and have been adding to that advantage through a robust field operation, are pollsters over-sampling Republicans?
Despite a raft of advantages in the electorate for Democrats, in September's first Gallup Tracking poll, an equal number of Republicans and Democrats were surveyed (including "leaners") from Sept. 3-5, compared to a 10-point Democratic identification advantage two weeks ago. That partisan makeup of the polling pool resulted in a 5-point lead for McCain in Sept. 5 tracking poll. Meanwhile, the new CBS poll features a 6-point swing in partisan composition toward Republicans, which plays some role in the poll's two-point lead for McCain. Finally, the latest USA Today poll, which claims a four-point edge for McCain, was arrived at after a 10-point swing in partisan makeup toward GOP respondents. read more.
Don't forget, it's all about the electoral college vote anyway.
I'd say they're also underpolling cell phone users (most likely Obama supporters) and college students (also most likely Obama supporters) and me. I've never gotten a pollster call but I'm one of those cell phone only peeps.
