Task: Question Answering
Input (English): Passage: In 1953, the Republican Party's Old Guard presented Eisenhower with a dilemma by insisting he disavow the Yalta Agreements as beyond the constitutional authority of the Executive Branch; however, the death of Joseph Stalin in March 1953 made the matter a practical moot point. At this time Eisenhower gave his Chance for Peace speech in which he attempted, unsuccessfully, to forestall the nuclear arms race with the Soviet Union by suggesting multiple opportunities presented by peaceful uses of nuclear materials. Biographer Stephen Ambrose opined that this was the best speech of Eisenhower's presidency. Question: Who called the Chance for Peace speech the best one Eisenhower gave as president?
Output (English): Stephen Ambrose