Two Dark Lords?

[Inziladun]

Originally Posted by obloquy

The act of successfully claiming the Ring would be all the battle necessary. To make the Ring one's own would require overcoming Sauron himself whether he was present or distant; once accomplished, this would sever Sauron's link to the Ring and Sauron would be defeated by that sundering. The result would likely be the same as with the destruction of the Ring.

What would be the requirements for a 'successful' claim?
The letter mentioned by Boromir88 indicates that Sauron would physically confront the claimant, with the victor being the Ring-lord, and the effect if Sauron lost would be the same as if the Ring were destroyed: for him it would be gone forever, with no chance of his regaining it. Simply saying 'The Ring is mine!' as Frodo did, obviously isn't enough to vanquish Sauron.