While this is a matter of opinion, I think that a very strong case can be made that Franklin D. Roosevelt left by far the boldest mark on US history during this time period. Roosevelt is famous for two major things. He was the creator of the New Deal, which was meant to help end the Great Depression. He was also president for the great majority of World War II. As such, he presided over the two greatest crises in the last 200 years of American history. Roosevelt's strong leadership during WWII did a great deal to hold the Allied coalition together. It also did a lot to help ensure that the war was won. This is surely something that leaves a "bold mark." In addition, Roosevelt is largely responsible for the huge increase in the size and scope of the national government. His New Deal, for good or for ill, laid a foundation for the assumption that the government would deal with all problems faced by the people. For these reasons, Franklin Roosevelt is my pick for the president in this time period who left the "boldest mark" on our history.