An ideology of lawlessness

Today's must-read is from Glenn Greenwald:

Isn’t it rather extraordinary to observe the Congress pass a much-debated bill [McCain's anti-torture bill] which the Administration vigorously opposed, and watch the President sign it into law, only for the Administration, on the very same day, to actually come right out and say that the President "may have to waive the law’s restrictions"?

Since when do we have a system of Government where the President can simply "waive" away laws?