Back in the 90s a group filed a lawsuit in OK, IIRC, contesting the 16th amendment. Something about it not being actually approved by the necessary number of states, and that they had evidence that the clerk or whomever in DC simply claimed it had been approved. Never heard much about it after that announcement. Wonder if the DSers got to them back then? The lawsuit got bounced by the Seventh Circuit, and SCOTUS denied cert.