Deliberate mistake: There is a huge security breach in the scene with Robin Williams and Christopher Walkin walking at night. The Security SUV limousine is more than 30 metres away from them. It should be pacing them in case of an emergency and be right next to them on the sidewalk. It appears the reason it is so far back is because at the camera angle the scene is shot at, it makes for a good background element which you would not see if the Secret Service followed protocol.
Continuity mistake: Right after the debate, we see Tom Dobbs and Jack Menken walking along the sidewalk talking. From the wide shot we see that they walk past the mail box on the sidewalk. Then when the camera cuts in to the close up, we see then walk past the same mail box again.