Given the thoughts and information in my head right now it’s a toss up between Truman and Johnson. From what I’ve been learning, the American industrialists and financiers who had been collaborating with the Nazis may have been treated extremely differently had Wallace been VP when FDR died - up to and including charged with treason. Instead, Truman oversaw the creation of the modern intelligence agencies headed by some of those very same Nazi collaborators, and gave the order to use nuclear weapons. Later on, JFK was resisting the entire intelligence and military complex advice on basically all foreign affairs, to the point where LBJ was getting briefings JFK wasn’t. The warmongers behind the scenes knew who would and wouldn’t listen to them. One of the last things JFK did as president was emphatically state that there would be no military action with regards to Vietnam. Then he got shot, Johnson became president, and all the MIC’s hopes and dreams came true.