Final answer:
The Constitution grants the president flexible powers within Article II, which establishes the executive power vested in the presidency, allowing for broad interpretation of presidential authority.
Step-by-step explanation:
The part of the Constitution that grants the president flexible powers is called Article II, specifically within the Executive Branch designation. This part of the Constitution, particularly phrases like "The Executive Power shall be vested in a President," has allowed for a broad interpretation of presidential power. Presidents often rely on the implication of their role as the guardians of the Constitution and their duty to ensure the laws be faithfully executed. This broad mandate can lead to differing views on the scope and limits of presidential authority.