https://en.wikipedia.org/wiki/Speech_or_Debate_Clause Presumably for this reason. However, the immunity isn't necessarily full. Although in this instance I imagine they would be all right.
Yea, it looks good legally. It's what let Gravel read the pentagon papers into the record without consequence even though they were classified. It's the justification people want Udall to use to read the unredacted torture report into the record so the rest of us can see it. The Obama administration would be on very shaky ground to try and prosecute a member of congress for informing the public on a matter that something that they thought was in the public interest. It's a fundamental checks and balance thing and it wouldn't be heard by a FISA court. It's also the kind of thing that could make it's way to the supreme court very quickly. The administration would either do nothing about it or a brave Senator would make a lasting legacy fighting off the depredations of the Obama administration and get a place in the history books. It's surprising that a tea party ya-hoo hasn't stepped up the plate already or it's not surprising that they aren't letting any tea party ya-hoo's see a copy of this agreement. It's surprising that the author of this piece seems unaware of the whole thing and thinks that Senators can be hoovered up into the justice system for speech intended to inform the public about issues that concern them.