 The president's demand came as he returned to the campaign trail. Mr Biden said he was thankful Mr Trump had not been badly injured, but also criticized his opponent on a number of issues. U.S. security officials say protection for Mr Trump had been increased several weeks ago after the authorities learned of an Iranian plot to kill him, something Tehran has denied. But they've stressed there's no known connection, the U.S. officials say, between Iran and Saturday's attack.