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Very simple version of the UET: The President can do anything that won't get him impeached and kicked out of office.
This is simply the Presidential version of Oliver Wendell Holmes's famous axiom: the law is merely a menu of what the government might do to you if you behave in such-and-such a way. Basically, if it won't cost us jail time or cash, it isn't against the law. Jaywalking is supposedly against the law. But if the cops won't ticket jaywalkers, as a practical matter it isn't.
Slightly longer version: The Executive -- not the just the President, all of them -- swears to "faithfully" preserve, etc. the Constitution. To do its job, it must frequently interpret the law. It cannot and should not rely on the other branches' interpretations, save possibly when there is case law precisely on point. Indeed, the "cases and controversies" clause prevents the Executive from consulting the courts. Therefore, the Executive's good-faith decision about the Constitutionality of a course of action is presumptively legal, and it should go ahead. If the other branches disagree, they have Holmes's remedy: punishment under the law. That means impeachment, trial and removal from office. That's the only stick the other branches have. This leaves two kinds of "high crimes and misdemeanors." The President can be false to his oath, especially interpreting the laws in bad faith, or he can refuse to leave the office when the time comes.
He's clearly interpreting the laws in bad faith. So let's get on with it. Let's impeach him and kick him out. Cheney, too, while we're at it.