The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States; he may require the Opinion, in writing, of the principal Officer in each of the executive Departments, upon any Subject relating to the Duties of their respective Offices, and he shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment.Don't think it won't happen. Especially if the White House gets word that Libby's about to turn on them.
And if that doesn't work,
But now I'm just upsetting myself. So let's all imagine for a moment that this will end the way we all hope it will. With the US Congress invoking another part of Article 2 - Section 4:
The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.