They've certainly banned 'Wrong answer responders' in other polls very frequently, the idea that there is any anonymity in responding to DU polls is a total fantasy.
This one isn't necessarily a moletrap as far as the basic results are concerned, a 1000+ poster could survive by expressing that the unhappiness was due to the O-man not being Left enough, not raping the rich enough, or letting himself be misled by advisors who weren't Progressive enough. Now, putting a comment in that 'I'm actually thinking of voting for the Republican instead,' THAT would get you banned.