Are Democratic primary polls actually rigged against non-white voters?

Probably not, but people are still making dishonest arguments that they are

Last week, the Washington Post’s political science blog, the Monkey Cage, had an article by Matt Barreto, a professor at UCLA, that alleged that polls of the Democratic primary were “undersampling” black and Hispanic voters, decrease aggregate support for the candidates they liked and thus keeping non-white candidates off the debate stage. All respect to Dr Barreto, but this claim is dubious at best and clearly diverges from the evidence we have available. The article is misleading in several ways, which I will discuss presently:

Representativeness depends almost entirely on the benchmark, and Barreto’s might not be the best one

Barreto “unskews” the polls by first using the American National Election Study (ANES) to create a baseline expectation for the racial composition of the Democratic primary electorate and then re-weights public polling data to match his targets. The math here isn’t necessarily wrong, but the benchmark very well might be.

According to Barreto, the ANES shows that …