Christopher Daly writes that a federal shield law protecting journalists' sources is unneeded:
Tempting as it might be, a federal shield law is a bad idea for journalists. We do not need it, and we may ultimately regret it. The relevant part of the First Amendment to the Constitution says: Congress shall make no law abridging the freedom of the press. That powerful simple phrase “no law” means just that – no law, period. It means Congress simply cannot legislate in this area.
As a near-absolutist about the First Amendment, I think that part is clear and simple. Furthermore, I believe that a proper reading of the First Amendment makes a shield law superfluous. We almost got such a reading in 1972, in the Supreme Court case known as Branzburg v. Hayes. In that case, the nation’s highest court said that when prosecutors haul reporters in front of federal grand juries and demand to know the names of their sources, the reporters must reveal their sources or face going to jail for contempt of court. In other words, reporters do not enjoy a legal “privilege” against having to testimony such as those enjoyed by doctors, lawyers, or clergy.
Sounds good to me. The "Congress shall make no law" phrase seems pretty clear-cut.