I'm all for a shield law to protect journalists and their sources from government prosecutors. I hope Congress passes one. But I don't have lots of faith that the ideas under consideration in Congress or any law can protect journalists adequately.
This is one of those areas where custom carries more weight than statute, the custom being the general good sense of prosecutors not to go after reporters for their information. For the most part prosecutors -- and by that I mean everyone from county attorneys on up--have refrained from going after reporters, including the notable and obvious exception of the Obama Justice Department. Yes, there are cases where prosecutors have gone subpoena-happy, from the BALCO steroids case to the Aurora shooting to the CIA leak case, where I was caught up in the maelstrom. But, generally, prosecutors don't pursue reporters even when they can. This unspoken compact began to become undone during the Bush administration, and, of course, it has unraveled during the Obama years as the national-security state has expanded.
This is something I know a bit about, having been subpoenaed in the CIA leak case. In 2003, I wrote a piece for Time, where I covered the White House, about how Bush administration officials were trashing Valerie Plame, the CIA operative whose husband was sent by the agency to investigate claims that Saddam Hussein was seeking to purchase uranium from Africa. Leaking Plame's identity was potentially a crime, and I was threatened with imprisonment for contempt of court for not turning over my sources. The case went all the way to the Supreme Court where it was declined. I've described my experiences at some length here, and here.