Trump’s first appearance was in a remote that aired October 1, 1986: Dave paid a quick visit to his office at Trump Tower.
Trump’s first guest appearance on Late Night was taped fourteen months later on December 2, 1987, and aired on December 22. He came on to promote his book he didn’t write, _Art of the Deal_. It being the run-up to the 1988 campaign, Dave asked if he were interested in running for the presidency. The story behind his feud with NYC mayor Ed Koch was uploaded here: https://www.youtube.com/watch?v=tych7G79U-I
Jimmy “The Greek” Snyder then guested on December 18 and discussed the prospects of a possible Trump campaign. (Snyder would be fired from CBS a month later.)