On "Palin/McCain" - What is the difference between a maverick and a loose cannon?

I agree with Mister J, so far only he he is the only one who actually knows what the term "loose cannon" signifies and gave you a good essment. "Loose Cannon" is derived from the day of wooden ships when an unsecured 5 to 6 ton cannon on a wheeled carriage would go careening across the deck when the ship rolled in the sea's crashing into anything that got in it was. You can rightly apply the term to James Carvel the Official Democratic Loose Cannon.