Mr. Duterte is not accustomed to being contradicted. Before his election to the presidency, he ruled his native southern city of Davao for two decades as a strongman mayor. Ghosts from those years have now appeared to haunt him. Two professed assassins testified in a congressional inquiry that they had taken part in hits ordered by Mayor Duterte and that the mayor himself had taken lives by his own hands. The later testimony, given by a retired police officer to corroborate the earlier one, has figured among the reasons cited in a Pulse Asia survey for the 7% dip in Mr. Duterte's approval rating to 76% in March, from 91% when he took office in July to 86% in October to 83% in December. The lawyer of the two whistleblowers is now preparing to file a case against Mr. Duterte with the International Criminal Court.