Final answer:
The administration of Franklin D. Roosevelt marked the shift toward a president-centered government with his New Deal policies and leadership during World War II.
Step-by-step explanation:
The turning point in American politics toward a president-centered government is most notably marked during the administration of Franklin D. Roosevelt (FDR). Prior to FDR's time, Congress was the main branch of the national government. However, with the advent of the New Deal and the various crises that faced the nation, including the Great Depression, FDR expanded the power of the Executive Branch. His leadership during World War II further solidified this shift towards a more powerful presidency, altering the balance of power between the branches of government to make the executive branch at least equal in power to the legislative branch.