FDR in better health

As everyone knows, Franklin Delano Roosevelt, the 33rd and longest-serving president of the United States, was in extremely poor health. He wasa long thought to have been crippled by polio, though recent evidence indicates he may actually have suffered from Guillain-Barré syndrome. Though he went to great lengths to hide the extent of his disability from the public, by the time he died at age 63, he looked 10-20 years older. In 1944, part of the reason why the democrats wouldn't renominate Henry Wallace was due to the high probability that Roosevelt wouldn't finish his term.

So my question is this: what happens if Roosevelt is in better health and lives longer, able to walk and not subject to a wasting disease. Does the Cold War still follow the same course? Is the atomic bomb still dropped? Are more atomic bombs dropped? How long does he stay in office? Does he have to deal with McCarthy? I assume he could stay as long as he wanted, so would he effectively be a dictator at the end of his life in oh, say, the mid 60s?
 
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