[Congress Members] shall in all Cases, except Treason, Felony and Breach of the Peace, be privileged from Arrest during their Attendance at the Session of their respective Houses, and in going to and returning from the same

The point is that it's literally Unconstitutional to restrict an elected member of Congress from entering the floor of the chamber. Well actually, they have legal immunity from any crimes they commit on their way to the floor for a vote - so if someone is detaining them and there's a vote going on, they could (hypothetically) get away with literal murder if that allows them to get to the floor.

Not saying I'm happy with that.