On NPR this morning, I heard White House chief of staff Bill Daley say, "The president cannot usurp the power that's in the Congress." What a relief! Also, this:
I don't think the American people would find it appropriate for the president of the United States to defy the laws of the nation and its Constitution, without their belief that that president should be impeached. And this president isn't going to do anything against the Constitution, against the laws of the United States of America.
So if the president were to defy, say, the War Powers Resolution by ridiculously redefining "hostilities," or if he were to defy the Constitution by signing a law that claims for Congress a power the Constitution does not grant (say, ObamaCare), we should impeach him. Got it.