Eisenhower was in the US throughout World War I, working on tank development so an accidental death amidst moving machinery, experimental explosives, engine fires and fueling accidents, would be a very reasonable POD.
The U.S. had hundreds of commanders, over 300 ahead of Ike in seniority in 1939, and much of the campaigns Eisenhower's credited with were far more the work of George Marshall (who had front line experience in the Phillipines War and World War I France where he quickly became General Pershing's right hand man/tactical planner.) Marshall very nearly headed the Normandy Invasion directly, the job was his and he really did want that one but his personal sense of duty to running the whole war kept him from it since he could literally assign himself to the job and would have been gleefully accepted by the British commanders he'd already been working closely with for 5 years already then. A 1943 Normandy Invasion and not a North African or Italian campaign are considerably more likely with Marshall directly in charge as that's where he wanted to start rather than the sideshows/diversions Churchill so fancied. Troop trainer Omar Bradley or Handy from Plans (Eisenhower's rising point) might step up, Patton would have a larger role and his understanding of terrain and logistics would get more play while his media frenzy problems that occurred in North Africa and Sicily would be avoided or postponed, Marshall was a friend and protector of George's from 1918 or so. Joseph Stillwell, Alexander Patch, Lucian Truscott, Walter Krueger, Mark Clark, Courtney Hodges, Walter Bedell Smith, there was an unusual amount of command talent that could have done as well or better in Ike's military roles. The defects in American diplomatic capacities in London and DC would have been more apparent with replacements more likely.
Ike's background in managing life or death complexities, infrastructure, logistics, the Pacific (Phillipines service under MacArthur in the 1930's), Europe, with Stalin, DeGaulle, the British Empire, post-war Europe, implementing innovations, the American Midwest and coming up from small town poverty rather than an affluent home made for an unusually effective Presidency. Marshall would have done as well and could have had the presidential nomination if desired (recall he had served as Secretary of War, Secretary of State, Chairman of the Joint Chiefs of Staff, was the a rare 5 star general, and his Marshall Plan for Europe gave him enormous credibility beyond any of the Generals who ran past or present short of George Washington.) Dewey's experience would seem irrelevant by comparison as would Adlai Stevenson's and he'd done more and better than Douglas MacArthur other than self-promotion. But without Ike and assuming Marshall didn't run and MacArthur self-destructed, it'd most likely be a Governor of New York or Ohio again as President for a less prosperous 1950's without the Federal Labs System, the Sputnik response, NASA's precursors, Strategic Air Command, NATO, Vietnam or Cuba OTL, the use of paratroopers to enforce Brown v. Board of Education school integration in Little Rock, the Interstate Highway System, nuclear power plants in the U.S., U-2 spy planes, maintaining the costly carrier task forces, backing the British & French down in Suez in 1956, the National Park System's major buildout), think of much more trivial accomplishments with a lot of belt-tightening after the war and New Deal's spending and far less interest in getting involved in any fighting outside U.S. borders. So the 1960's & 70's would be far different as well.
