Look at the photographs of President Franklin D. Roosevelt shortly before his death and you will find an exhausted man. It surprises many to discover that FDR was only 63 years old when he died but anyone who studies his presidency may be amazed that he lasted that long.
Franklin Roosevelt was a brilliant leader but his management skills were terrible. An adept manipulator, FDR intentionally created chaos. He often assigned the same task to more than one Cabinet officer and even at the best of times his Cabinet was not a happy crew. He encouraged rivalry, took on a massive workload, and maintained a White House staff that was almost nonexistent. [A previous attempt to reorganize the executive branch had been blocked in Congress before the war.]
And then the war came. By 1944, there were 47 war agencies reporting directly to the president. When he arrived at the Yalta Conference to meet with Churchill and Stalin, his health had declined so greatly that the British were shocked at his appearance. Lord Moran, Churchill's doctor, said, "I doubt, from what I have seen, whether he (Roosevelt) is fit for the job here."
That observation was made on February 4, 1945.
President Roosevelt died on April 12, 1945.