While the best con is one in which the victim never even realizes they got scammed, that can seldom be guaranteed. So the con artist needs a final argument to make to their mark if they get confronted, and the one they often use goes as follows: Sure, I conned you. But this is your fault. You were dumb enough to believe me. Now get lost, sucker.
That is what President Donald Trump is now saying to the American public on the subject of his tax returns. He spent years saying that he would be releasing his returns as soon as a routine IRS audit of them was complete, so the American public could understand exactly where he gets his money and where he might have conflicts of interest as president.