When Congress allows its own subpoena and oversight powers literally to be ignored and scoffed at, the damage to our system of checks and balances can't be overstated. The whole premise of our system of government is that executive lawbreaking and presidential corruption is checked primarily by Congressional oversight. If Congress can't or won't compel the disclosure of information, then it can't investigate anything, and the President has no meaningful checks on his behavior. It's really just that simple.