Russia has consistently denied any involvement in Mr. Navalny’s poisoning, at one point alleging that he could have been poisoned in Germany. On Thursday, Mr. Putin suggested the attack could have been an elaborate ruse to increase Mr. Navalny’s prominence. “The trick is to attack a leading figure,” Mr. Putin said. “It is well known that this trick of political battle is used around the world.” The marathon news conference —this one lasted four-and-a-half-hours — is a longtime tradition for Mr. Putin, a way for the Kremlin to put his stamina, his accountability and his authori...