The right to bear arms has survived more than 200 years without infringement, and this is the major basis of the NRA's campaign to permit the legality of assault weapons.
A number of "firearms" have been established as illegal for private ownership, including the submachine gun, the Browning Automatic Rifle and dozens of foreign automatic and semi-automatic guns.
If "arms," as used in the Second Amendment, cannot be "infringed," how did these firearms happen to be declared illegal for private ownership? The Second Amendment establishes militias with no mention of individual arms ownership.
The point is that the Second Amendment can be easily challenged and can be done to restrict AR-15s.