What is a session?
Another case that went the other way (because he was a Republican) was Idaho Senator Larry Craig. Craig was arrested at the Minneapolis Airport and charged with lewd behavior for soliciting gay sex in a men's room. Craig said he had a "wide stance" and accidentally touched another man's foot while standing at a urinal.
Craig pleaded guilty to the misdemeanor charge of disorderly conduct, but later tried to retract his guilty plea when it was pointed out that he might have had immunity based on the "going to and returning from the same" clause in the Constitution. However, I'd think that a solicitation charge might fall under the "Breach of the Peace" exception, unless that's for public drunkenness (in 1789) and participation in unlawful protests.
-PJ