The addressee was certainly correct in holding their ground over the 13 cents "postage due" the USPS wanted to charge. But the effort to go to the post office and meet with the Postmaster about it cost more than the 13 cents to begin with.
http://www.csmonitor.com/The-Cultur...-of-13-centsI wonder if he kept the cover? A postage due notation on a Presidential signed piece of mail would certainly be a conversation piece.