Sit in a slowly-moving convertible and let an ex-Marine sharpshooter take three shots at you with a MC (using real ammunition) if you think it's such a piece of harmless junk. Does he seriously think it's impossible to kill someone with that "joke" of a rifle from a distance of 88 yards?
When the FBI tried to duplicate the shots, they needed to add 3 shims to the scope to even hit the target. A sharpshooter would NEVER use a misaligned scope, especially if he planned to assassinate the POTUS.
So, the answer is no, it would not have been impossible to kill someone with that MC, however, hitting a moving target 2 of 3 times including a headshot at 88 yards, looking thru the wonky scope of a crap rifle is so improbable we should be able to rule it out, like Wecht does.