I don't think this song is about Bush:| he isn't even American, so it'd be non-sense to a British person write a song about an American president!
In my opinion, he sings about a prepotent person that used to imagine he ruled the world. Now he sees himself lonely, like nobody liked him anymore.
After thinking about it, the line "The old king is dead, long live the king" could be a reference to Jesus being on the cross. All of the people mocking him, and King of Jews above his head.
It's an awesome song! :)