It is legal; however, it was misrepresented multiple times to Congress including recently. Watch the video on the ABC News page, and you can see for yourself how Congress was lied to concerning how it would be implemented.
As for blank's saying that the buck doesn't stop with the President, Obama DISAGREES with blank. He defended his position on it today:
Obama: ‘Nobody Is Listening to Your Phone Calls’ - ABC News
He is correct that no one is listening to the actual call - that would take too long. The metadata that he is referring to for phone calls is correct; however, it is not the same for internet communications and email.