Attorney General Jeff Sessions recused himself from the Russia investigation. That is the investigation that Sessions promised to stay away from. Firing the man heading the investigation — especially if Sessions knew that the reason was not the one stated in Deputy Attorney General Rod J. Rosenstein's May 9 memo — is a matter "arising from the campaigns for President of the United States." Sessions may have some explanation for why he chose to participate in the firing of Comey. But the attorney general may now be in considerable legal peril.