Just saying that this poll is composed of 10% or so more Democrats than Republicans, but this is still trouble for Don
First of all, there are more Democrats than Republicans in this country at present, so this is reasonable. Would you contend that there should also be as many Libertarians sampled as Democrats and Republicans? Second....
Begin: soapbox
I'm not going to quote the whole thing, but this is correct. Party ID is an attitude, not a demographic, and plenty of professionals have been burned by thinking otherwise, as recently as 2012.