Congress is not "above the law", but then again, neither is the Executive nor the Judiciary.
if this decision had gone the other way - it would have been. it would be the only branch to have a constitutional protection against oversight from the other branches. and not for legitimate actions mind you, I agree that is in the constitution - but for EVERY KIND OF CRIME. the executive and judicial bracnhes have impeachment and removal, so who oversees congress if the law were to be as you suggest?
and don't answer with - "the voters", or "they investigate themselves".