Depending on the details of the contract
it could be within Disney's rights to block commercial distribution in the US. It would be a shame if they took that route.
I'm not typically a Moore defender (although for that short-lived TV series of his - forget the name - he came up with some hilarious bits), but Disney's explanation rings hollow for me: "It's not in the interest of any major corporation to be dragged into a highly charged partisan political battle." Surely they knew going in with Moore that the object of the project was to stir "a highly charged partisan political battle."