It's a grey area. Nixon was in Dallas 11/21 criticizing Kennedy. He either knew what was to happen the next day or was unknowingly sent there to be set-up for future blackmail.
In late November of 1963, Pepsi scheduled a corporate meeting in Dallas, Texas. This meeting coincided with a national soda pop bottlers convention there. Pepsi invited former Vice President Richard Nixon to Dallas for the corporate meeting. While he was in Dallas, on November 21, 1963, Nixon gave a press conference in which he criticized the policies of President John F. Kennedy.