When approaching the Marine One helicopter, the President salutes the marine at the foot of the steps leading into the helicopter, and the marine returns the salute. This is the complete reverse of what should happen - the marine should salute the President, the Commander-in-Chief, not the other way round.
In some materials for this film, notably the Directv "Cast and Crew", Gloria Reuben's character is listed as "Delores Meriwether". Yet Michael Douglas's character Agent Garrison clearly refers to her as "Nancy". While in still other cast listings, she is listed as simply "Mrs. Meriweather". Clark Johnson who plays her husband is listed, alternatingly, as "Charlie Meriwether" or "Mr. Meriwether".
In the first exterior scenes where Marin and Breckenridge arrive to investigate the murder, she's wearing a tight low-cut black shirt under her jacket; when she comes out of the same house in a later scene (same point in the narrative, during the initial investigation) she's wearing a loose-fitting striped collared shirt under her jacket.
When Agent Garrison is at the house of murdered agent Charlie Merriweather, the widow points out a red Cadillac suspiciously parked outside her house. When the red Cadillac leaves the left upper tail light is burnt out. In the next scene when Agent Garrison is following the vehicle, the left tail light is functioning properly.
When Garrison arrives at the White House after the coffee shop and is asked where he was, he states that the departure isn't scheduled until the next day. Later when being questioned in his apartment, he states that it was only moved up 2 hours.
In the first shot when the presidential helicopter "Marine
One" gets hit by the missile, you see the missile and its smoke trail. In the following shot where the helicopter explodes, the smoke trail of the missile is gone.
When Jill Marin shows her identification to the security camera and walks through the doors to the reception desk of David Breckinridge's office. The door she opened and walked through stays open behind her but on the security monitor you see the door closing as she passes through. In the next scene the door is closed.
When Garrison is being chased by Breckinridge towards the out-of-commission ship, the camera zooms in on Breckinridge's foot stepping in a puddle before it changes cameras to see Garrison inside the ship. Once he gets inside, Breckinridge descends a flight of stairs and the camera does the same zoom on his feet again, but his shoes and pants are perfectly clean.
Pete Garrison is hiding behind a green WM (Waste Management) trash bin in the first chase scene. The registration number is visible on the trash bin and it starts with "CA", indicating it was distributed in Canada, not Washington DC where the movie is supposed to take place.
When Pete takes a phone call outside the Mayflower Hotel and the caller tells him to go to Massachusetts Avenue, then walk to 12th street, Pete goes the wrong way down Connecticut Avenue. He walks toward L Street. Massachusetts Avenue is in the opposite direction, up Connecticut Avenue.
When Agent Marin describes how a downed agent's gun still had the safety activated, she is referring to a Secret Service issue Sig-Sauer P229, which has no safety lever to deactivate. It instead has a decocker, which increases the length and pressure of the trigger pull but does not prevent the weapon from being fired. Typically, the weapon is carried in the holster decocked, and the agent would fire the first round double-action, followed by single action for successive shots.
Pete Garrison's national security adviser requests a list of personnel with "Q" clearances. Q clearances are granted strictly by the Department of Energy and are the equivalent to other agency's Top Secret clearance. Instead of dealing with encryption as the national security adviser mentions Q-cleared employees deal with nuclear power and weapon capabilities.
The standard sidearm of the Secret Service is the SIG Sauer P229 chambered for .357 SIG rounds. The sidearms used in the movie by the agents are clearly SIG Sauer P228s, which are only available chambered in 9mm rounds.
The rear passenger doors on the 2006 Cadillac DTS presidential limousine are not as far back as the ones on the limousine portrayed in the movie. On the real presidential limousine, the doors are located at the third window from the front, not the fourth.
A suppressor does not significantly reduce the velocity of a bullet. A suppressor works by redirecting and cooling gases already released from the muzzle of the gun, therefore these gases would not be further propelling the bullet regardless of whether a suppressor is used.
The terrorist leader complains to his contact about the attack on the helicopter via a mobile phone. When he finishes the call a dialling tone is heard, but mobile phone services do not use a dialling tone.
The goof item below may give away important plot points.
When Breckenridge is examining the body of Agent Merriweather, he lifts a brass casing from beside the body. The shooter was at the foot of the stairs and a casing ejected from his gun would not have traveled forward and ended up next to the body. It would have been found to the right or behind where the shooter was standing.
When the Marine HMX-1 helicopter is shot down, the news reports repeatedly refer to the helicopter as "Marine One", while saying it is not known whether the president was on board. In fact, the call sign "Marine One" would not be used unless the president is on board.