Bullet-proof vest wouldn’t have saved him as he was sniped in the neck. The head is a moving target and harder to hit, which is why the less professional sniper missed Trump, he tried to shoot him in the head and Trump happened to move his head at that very second, and aiming for center of mass can be risky in case they are wearing something bullet proof. The neck is clearly exposed and more stable of a target than the head. The sniper knew what they were doing.