this time i wont try to impart my own constitutional analysis. Im in law school, but im focusing more on other things, so my knowledge of con law isnt as sharp as it will be next year when i sit for the bar.
so here is some legal analysis that sounds more accurate than mine courtesy of Volokh.com
http://volokh.com/2003_09_28_volokh_archive.html#106494751387414760">Volokh analysis
Volokhs main conclusion: "The rule in criminal cases is at least as pro-disclosure, and probably even more so. Since this evidence is critical to identifying who may have violated the law, and since it's hard to see how prosecutors can realistically uncover it without asking Novak or one of the other reporters, Novak probably won't have a privilege"
(I know its more of a right wing site. Disregard the other nonsense, but read the legal reasoning. This author believes Novak might just be forced to reveal.)