Article I Section VI

They 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; and for any Speech or Debate in either House, they shall not be questioned in any other Place.

I do not know the whole story regarding the Cynthia McKinney case. I do not know in what fashion she struck the officer. I do not know where she was going at the time. It could very well be that she deserves to face charges.

On the other hand, I do know that under certain circumstances she had every right not to be stopped.
And I know that the comments by many of the GOP are flat out wrong in that context. I know that the Congressional Representatives and Senators are exempt from these checkpoints under the US Constitution; I know the only way to change that is to amend that document.