You don’t impeach Senators.
(copied from the top center in the link below)
https://www.senate.gov/reference/Index/Impeachment.htm
Tar and Feather is approved!
That's too good for traitors. Turn them over to the Hague for war crimes (arming known terrorists, supporting the overthrow of legitimate governments). How about Sedition, (ex: leaking classified information) for actions that undermine the policies of the US government? And while we're at it, has McCain violated the Logan Act by undermining the policies of the US President at an international meeting of governments?
I wouldn't mind settling for McCain spending the rest of his life in a locked room with padded walls. But prison for the rest of his life for war crimes and treason would be so much sweeter.