Joe, the Bush administration IS responsible for lifting the nation-wide ban on concealed handguns in national parks. And no, he did not need to enact legislation for this. The Interior Department promulgates regulations for national wilderness areas--without Congressional approval. (Congress delegated the power to regulate the interior to the executive administration a long time ago.)
In any case, yes, the Bush administration (and Bush, if the "buck" even passes through his office anymore) is responsible for lifting national bans on mountain-biking, guns, etc., in the parks. The parks, and states, though, still have the authority to enact their own rules regarding these matters, so it's doubtful if mountain-biking will be allowed on the JMT. Guns most certainly will not be.