They only do it with the effective Republican presidents, such as Nixon for Watergate, Reagan (threatened for Iran-Contra) and now Trump (grab bag of legal non-offenses). Ever remember them moving against GHW Bush, GW Bush or Gerry Ford? Of course not, because they were “good guys” who didn’t rock the Establishment boat and who were totally ineffectual as presidents.
They wanted to impeach George W. Bush, but the leadership did not.