They have played the "race" card, the "Romney is too rich" card, the "Romney is a tax cheat" card, the "Romney killed a man's wife" card, the "Romney want you all to be put back in chains" card, the "Romney wants bad air and bad water" card, ad nauseam, et cetera.
Problem is that at some point you run out of cards.
And in poker, you can only play a card once.