WASHINGTON—Defending her performance against recent reports of cognitive decline, senior United States senator Dianne Feinstein argued Friday that she was still perfectly mentally fit to continue captaining the submarine. “If my fish colleagues have any doubts about my ability to damn the torpedoes or up the periscope, they simply haven’t told me,” said Feinstein, who admitted that she had briefly forgotten her first lieutenant’s name during a meeting at his battle station before blaming it on stress related to enemy ships rapidly pinging on radar. “Until I hear a compelling reason why I should step down as captain of this ship, I’m afraid I’ll just have to chock up these rumors to a mutiny brewing among my crew.” Feinstein declined to discuss her retirement, stressing that even if the submarine should spring a leak, she was prepared to go down with the ship.