President Trump should be savoring the end of Special Counsel Robert Mueller’s investigation with no charges of collusion or obstruction of justice, but as ever he can’t stand prosperity. His post-report scrap with former White House counsel Don McGahn shows how this President is so often his own worst enemy.

As part of his obstruction “analysis,” Mr. Mueller recounts that in June 2017 Mr. Trump asked Mr. McGahn to ask Deputy Attorney General Rod Rosenstein to say Mr. Mueller had conflicts of interest and couldn’t remain…