UNLESS (only unless) Tenet decides to strongly support President Bush's re-election.
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I have a feeling that he will. In fact I think it's as likely he's leaving so that he can speak openly and freely about issues that may well help the President. Imagine what he might have to say about Plame, Iraq intelligence, September 11, etc. without being handcuffed by the politics of his position as CIA chief. It would be quite amusing, as Pelosi and the gang defend Tenet as a victim and say he shouldn't be the fall guy, to have him come back on the attack.