What if...
The US responds to the rise of Totalitarianism in the early 1920s by drafting, passing and ratifying the 22nd Amendment to the US Constitution 25 years early after having just ratified the 17th and 18th Amendments. Thus FDR cannot seek a third term as President. I would presume that "Cactus Jack" Gardner would then become President and be the man who won World War II and confronted Hitler and Tojo. Gardner, who was willing to try the improvisation of the First New Deal in desperation at the crises of the Great Depression, was an unequivocal opponent of the Second New Deal while helping to organize opposition to the attempts at Court Packing. FDR would have left office with the US still mired in the Great Depression and may well be remembered as a popular and well-meaning failure.
How would American Domestic politics have been altered by a very different man being the hero of anti-fascism and the man who ended the Depression? Many of the men who turned out to be Communist spies would likely have been purged out of a Gardner Administration fairly quickly for purely political reasons thus resulting in no Hiss-Chambers Controversy, no Richard Nixon and no Joe McCarthy. Eisenhower's entry into politics would have unquestionably been different, even if just as a function of the electoral calendar.
How would the Cold War have unfolded with a President more vigorous than FDR and more experienced than Truman at the helm during the key moments when Stalin was seizing various advantages? At least part of the Marshall Plan was about shipping abundant American food stuffs to Europe for the benefit of voters in swing states amid the dislocations of de-mobilizations, so the saving of Europe from post-war starvation would have still happened. Gardner's advisors would have been more Jesse Jones and less Henry Wallace.
Additionally, Gardner spoke with JFK on the phone the morning that he was assassinated. Gardner lived seemingly forever and would have hovered over American politics as a towering hero for 20 years in a manner that no popular former American President has during the 20th Century. Teddy Roosevelt cast a significant shadow but he still died in 1920, only 11 years after he left office and he was more of an outsider than Gardner would have been. Men like Truman, Nixon, Ford, Carter, Bush and Clinton did not exist post-White House as national heros. And only Johnson and possibly Nixon were as firmly embedded in the machinery of national politics prior to becoming President.