Is it true that “Most polls misrepresent the Democratic electorate” and that this “skews the results”?

Someone pointed me to this post in the Monkey Cage, a political science blog that I participate in. The post was about non-representativeness of political polls, and it had one good point and one bad point. Overall I think the claims in the post were overstated. CONT.

Andrew Gelman (Columbia U.), Statistical Modeling, Causal Inference, and Social Science