Why aren't Congressional members subject to screening?

Rep. Cynthia McKinney (D) is accused of punching an officer who attempted to stop her from bypassing Capitol security. Apparently the officer didn't recognize McKinney, who does not have to go through screening like the peasants do. You'd think that the policy would have changed after this incident in 2003, when a New York City councilman was shot and killed by someone who got to bypass security. You and me, we get the cavity search, but the royalty gets to just cruise on by.