When confronting the hunters in the opening scene, Swagger tells them that the .223 Remington cartridge is not suitable for anything larger than a squirrel. While not a big-game round, it is essentially the same high-velocity rifle ammunition used in the AR-15/M-16/M-4. The statement would have been true about a rifle firing the .22 LR (Long Rifle) round, which has a muzzle velocity less that 50% of the .223 and a bullet that weighs 1/3 less.
Issac says that according to the letter found in killed agent's pocked, president will be killed in 21 days during a visit to the Science Centre. The the letter (shown fully on screen) never specifies the place, only states that 'Angel of Death' will kill president within 30 days.
When the Ukrainian president was shot, people behind the fence starts screaming and put their heads down.
But Chinese lady, behind the kids in first row, is smiling which is unusual for this situation.
When going over the anticipated threat with the Secret Service, Swagger explains the window of opportunity in terms of the distance between the car and the building and the average circumference of a human head. Circumference is the distance around the outside, and the number cited (22 inches) sounds about right; but the size that matters is the diameter, or the distance across, which would be close to 7 inches.
When Bob Lee is looking at the sniper rifle 23:52 in, he is clearly shown using an adjustable wrench on the weapon. Neither a Marine-trained marksman or a sniper would use this kind of wrench on a weapon unless in extreme circumstances. They would use a properly sized wrench.
After the raid on the Russian gangster, Isaac Johnson checks Agent Memphis' badge, but doesn't return it, and the gold of the shield is still visible in his hand as he walks away.