Some guy cuts in line in front of me at the check-out. Under the freedom of speech clause of the Constitution, I can question the legitimacy of his birth, point out his canine maternity and his Oedipal tendencies. I'm perfectly within my rights to do that. But, that doesn't consider the consequence, that he can bust me in the nose. He may not be within his rights to do that, but he can. And, he'll suffer the consequences.
Don Imus made some remarks that he was perfectly within his rights to make. But, he didn't consider the consequences and was fired for being inconsiderate, of the people he was talking about and of what could happen to him.
The law says I can't drive my car without the registration sticker. When I took off the old sticker to put on the new one, I thought about that. I cranked up the car, drove it around the block a few times. It ran just fine without the sticker. So, I can drive my car without the sticker. But, I must consider that it is illegal to do so, and if caught, must suffer the consequences.
George Bush can fire any or all of the US Attorneys he wants to. He has done that. But, just as I must drive my car legally, he must fire attorneys legally. Firing attorneys for investigating criminal activity is obstruction of justice, a crime. Just because you can do it doesn't make it legal.
The difference between me and a high-falutin shock jock with a ridiculous hat, and a President who is ridiculous without a hat, is that I must consider the consequences of what I do, and they feel that they are immune to consequences. Imus found out that he's not. Bush is finding out that he's not, either.