Final answer:
After Abraham Lincoln, the two presidents most recognized for expanding the power of the presidency were Franklin D. Roosevelt, during the Great Depression and World War II, and Theodore Roosevelt, who advocated for a strong executive role through his 'Stewardship Theory.'
Step-by-step explanation:
Expansion of Presidential Power After Lincoln
Following Abraham Lincoln, the two presidents who notably expanded the power of the presidency were Franklin D. Roosevelt (FDR) and Theodore Roosevelt. FDR expanded presidential power greatly during the twin crises of the Great Depression and World War II. His policy interventions and leadership style during these times allowed him to eclipse Congress and push for an expansion of the federal government's role in the economy and society. Theodore Roosevelt also enhanced the power of the presidency through his activist approach and the notion of the 'Stewardship Theory,' which argued for a strong executive role. Both Roosevelts employed the broad interpretation of the 'executive power' outlined in Article II of the Constitution to justify their actions, which were not specifically enumerated in the document.
Theodore Roosevelt's influence is additionally notable for reinforcing the trend that the chief executive is most powerful during wartime, as he took action in various military affairs without the approval of Congress. FDR's extensive use of executive orders, his unprecedented four-term presidency, and his role in expanding the federal bureaucracy, like the Secret Service and Federal Bureau of Investigation, contributed to increased presidential influence.