Unless you submit that there is no criminal activity that can bring a Congressman under legal jeopardy if it takes place in his office.

Uh, Tom, pause a moment, and remember what Article I.6 says: "They shall in all cases, except treason, felony and breach of the peace, be privileged from arrest..."

The problem isn't blanket immunity, it's the sticky problem of how to conduct an investigation of a Congressmen that fits within the letter of the Constitution. The intentions of the Founders are beyond dispute: They wanted to protect the Legislative branch from potential misues of the Executive's police powers. If you try and say that all investigations are OK but that only the actual arrest is constrained by the Constitution, you open up the door to bigtime harrassment and intimidation, and fishing investigations for politically-sensitive information (which the FBI, to its credit, took pains to avoid, in this case). Investigation before arrest is, in this case, a real chicken-and-egg problem.

By all accounts this is the first time in over two centuries that Article 1.6 has come up. Wouldn't be the first time that we discovered a few sentences in the Constitution that, when needed, don't provide the crystal-clear guidance we'd like.

And that's why this may legitimately end up in the Supreme Court. It's exactly the sort of question they were chartered to decide.