A good question is, 'Why did Bush order the law to be broken, when he could have gotten any legitimate authority through the FISA court?' One part of the answer, which probably remains beyond the imagination of most, is that it was always the intention of Bush, under the guidance of Dick Cheney, to turn the 'Presidency' into a Dictatorship. This is the form of government they think is proper. Therefore Bush breaks laws because he needs to do so to establish that this is a Dictatorship. We have built gradually towards this; now it has built to where Bush has asserted his powers openly.
He wouldn't have opened up if his activities had not been revealed, but he could have continued to deny, and the 'news' media would have mostly dropped the matter after a short interval, like they have everything else. Bush decided not to deny, though, because he (alone or in consultation with whomever) saw it as a moment in which to solidify Dictatorial authority.
Nixon eventually claimed similar powers, but was alone. His attorney was embarrassed and said only that he was told to argue that Nixon had Dictatorial powers. It was laughed out of court. Nixon caved and of course resigned in disgrace.