We find in the Constitution that he is immune from prosecution when he is in DC.
Section 6. The Senators and Representatives shall receive a compensation for their services, to be ascertained by law, and paid out of the treasury of the United States. 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.Of course, as Daddy's son he is typically exempt from prosecution anyway. Daddy got away with manslaughter. Patrick considers it a birth-right.
Y'all want to impeach somebody? Patrick might be a good place to start. The Senate has never had the balls to impeach Teddy. So much more the shame. I'm becoming convinced that no one in either deliberative body has a moral compass worth following.