Donald Trump Signed His Presidential Oath Before Election Day

Donald Trump will be repeating himself when he takes his presidential oath this week, because he already did it ... long ago.

Trump slapped his autograph on a faux Presidential Oath of Office doc -- with the full text -- back in November of 2015 during a rally in Worcester, MA. We're told a supporter wrote it up and had him sign.

He was all smiles when he signed it ... seeming pretty confident it would all come to pass.

The gag document is now hitting the auction block with the help of Moments in Time.

Starting bid is $3,500, but the auction house is banking on 6 times that amount.