Since the fish tank was CGI, Chace Crawford had to rehearse the tank scene about 25 times before they were confident enough to get the shot. The shot used was the first take.
The fish tank that The Deep hits and destroys was done all by CGI. Chace Crawford had to mime hitting a fish tank with the tank itself being added later with special effects. Since water typically looks fake on an actor when done by CGI, a crewmember had a water lever ready to be pulled as soon as Crawford "broke" the glass.
The fight scene took 10 days to film.
The assassination is planned for Washington, DC's fair grounds, but as DC is not a state it only recently started having a "State" Fair and thus has no fair grounds.