Question

Under whose presidency were the relations between the president and congress and the nature of presidential leadership altered?

Answer 1

Under Franklin Delano Roosevelt, the American presidency wielded more executive powers in what scholars have referred to as the modern presidency.
Prior to his presidency the executive office was more subservient  to congress with most legislation emanating from the houses. however during Roosevelt and after, the presidency has become a focal legislative office, wielding unlimited foreign, and domestic policy powers.