The Trump presidency has been consumed by Special Counsel Robert Mueller’s efforts to uncover collusion between the Trump campaign and Moscow. Mr. Mueller reportedly has secured one or more indictments that he will announce Monday. Some Republicans now seek a new special counsel to investigate if the Clinton Campaign “colluded” with Russians to smear Candidate Trump, along with other aspects of the Clintons’ relationship with Russia and Russian nationals. But one special counsel already is one too many.

During the 1980s and...