Trivia

In one of the behind-the-scenes featurettes for the film, a Secret Service consultant to the production stated that actress Eva Longoria far surpassed the other actors in "shooting school". In fact, he remarked that her score would beat about 90% of members of the Secret Service. Longoria mentioned that when she was younger she often accompanied her father to the gun range, so being around and handling guns wasn't new to her.

As screenwriter George Nolfi honed the screenplay, producers Marcy Drogin and Michael Douglas brought in Clark Johnson to direct. Johnson had previously directed a pilot for a series about the Secret Service called Secret Service (1992) [See episode: The Stalker/Bomb Protective Mission (1992)] which pointed to his interest in the topic. Johnson, also a respected actor, had worked in almost every area of the film business, including stunts, special effects, and camera. In addition, he was experienced with law enforcement action thrillers, ensemble pieces, multiple cameras, large set-ups and special effects. For The Sentinel (2006), Johnson used this extensive background to depict the reality and grittiness of the Secret Service world.

The meaning of the password "CRYSTAL" was "follow my orders".

Actor Kiefer Sutherland responded with equal enthusiasm about co-star and actor-producer Michael Douglas as the latter had said of him: "If you look at Michael's films, they're Class A. I had the pleasure of working with him when I was very young, and he was so gracious and kind to me. I watched his films over the years and learned what makes him a phenomenal producer. There's a sense of responsibility and dignity in all his films. I've watched his table-read, his notes, how he handles himself on set. It's been an education and a pleasure, and I'm grateful for that."

Star Kiefer Sutherland's, like the other cast members, enjoyed having an actor as a director with Clark Johnson. Sutherland said: "There is a commonality there. That's undeniable. Clark has an innate sensitivity and that's a two-way street. To know what it's like to work in your shoes is a gift."

Clark Johnson: Agent Charlie Merriweather at the start of the film. Director Johnson cast himself as Agent Merriweather, who has inside information that he is silenced from sharing, and whose murder uncovers the plot to kill the president.