[Lancey Howard]

Yes, the Constitution says that Congressman may run criminal enterprises from the safe haven of their congressional offices, and there’s nothing anybody can do about it.

[muawiyah]

Whether they can or not the court said the raid itself wasn't unconstitution ~ merely meaning that presumably raids could be conducted ~ but the materials taken weren't all of a nature that can be taken. The court wasn't asked to describe how a raid could be conducted on a Congressional office where protected and unprotected materials may well be intermixed, but that's for a later day and a different court (the Supreme Court). You will notice, though, that Jefferson was unable to wrap around himself the protections applicable to Congress.

Which means, of course, that constituent letters were untouchable as were secret messages from the then Democrat majority leader in the House, or other Democrat caucus officers.

FBI didn't care ~ they read your mail anyway. It's still yours years after you send it to somebody you know.

Did they get a warrant on probable cause that your correspondence to this guy was part of a crime?

What you have here is a court that made the minimum decision possible to allow the cops to look at some of Jefferson's stuff while not also suggesting that the cops broke the law and should be punished (which is what I think the Supreme Court will say whenever it gets this or a similar case).