According to "Stamford transgender person charged with sexually assaulting minor" Stamford Advocate June 8, 2011:
A city transgender person was arrested early Wednesday morning after police say she sexually assaulted a teenage boy at Stamford Town Center in April.
Isaiah Johnson, 20, of 202 Ursula Place, was charged with second-degree sexual assault and is being held in lieu of $25,000 bond.
Youth Bureau Sgt. Dedrich Hohn said Johnson, who is known to patrol officers in the South End, was picked up at 2 a.m. Wednesday on Atlantic Street near Veterans Park, where she met with the youth before the April 26 incident. Hohn said the patrol division was alerted to Johnson's arrest warrant Monday night. The victim is a student with special needs, Hohn said.
Hohn said after meeting the youth just after 7 p.m. at Veterans Park on that April night, Johnson allegedly lured him into a men's room at Stamford Town Center.
The assault occurred in the men's room, Hohn said. Police secured videotape of the two going into the bathroom.
Hohn did not provide details on what allegedly occurred in the bathroom. Second-degree sexual assault involves sexual intercourse between someone 13 to 15 years old and another person more than two years older
Senator Craig on the other hand plead guilty to "disorderly conduct", which is not a sexual offense. He allegedly extended his foot and part of his hand into an adjacent stall when using the restroom. But even if you consider what Senator Craig did "sexual misconduct", the statement in the OP is still false.
Edit: some have expressed interest particularly in women's bathrooms even though the OP is generic as to men's/women's/family etc. No senator has been arrested in a women's bathroom; however:
From the Brooklyn Daily Eagle 28 January 1929, page 22:
Stephen Wiszak, 24, of 312 E. 12th St., Manhattan, was arrested last night on a charge of felonious assault at 101 Allen St., Manhattan, where he had been pursued by a crowd. Garbed as a woman, wearing an expensive seal coat, Wiszak is alleged to have beaten an unidentified woman with a revolver In the women's rest room of the Rivington st. station. of the 2d ave. elevated rd. Detectives Schneider and Sargeant Brough of the 5th st. station, who captured Wiszak, questioned him In connection with the murder of Mrs. E. Weigand, whose body was found in the washroom of the City Hall station of the B. M. T. on Aug. 5, 1927. A woman told John Dougherty, change agent on the northbound platform of the Rivington st. station, that a man dressed as a woman had followed her that into the washroom, bolted the door behind him, tightened a scarf about her heck and when she struggled beat her on the head with a revolver. She struggled so desperately, she told Dougherty, that her assailant released her and fled. Dougherty believed from the woman's actions that she was intoxicated. Going to the street, her appearance attracted a crowd, to which she related the occurrence. When Wiszak appeared on the street the crowd gave chase. Wiszak took refuge in the Allen st. house, where he was captured.
There is another account of the story in the Reading Times 29 January 1929, page 7:
...She had told John Dougherty, ticket agent on the northbound platform, how a "woman" in the washroom had choked her with her own scarf, and beaten her over the head with a revolver barrel. She said her insistent struggles finally won her freedom. Dougherty thought she was drunk. The victim went to the streets and a crowd heard her story. Wiszak came down the stairs and the crowd pursued him - into a hallway. There detectives arrested him. The woman whose story led to the chase had meanwhile vanished. Wiszak, who fought under the name of Young Eddie, was painted and powdered and wore a sealskin coat, black silk turban, blue flowered dress, flesh colored stockings and tan pumps. He said he had no occupation.