Which role does the Vice President assume if the President can no longer serve?

The Vice President assumes the role of Acting President if the President is unable to serve, due to reasons such as incapacity, resignation, or removal from office. This succession is defined in the Presidential Succession Act and affirmed by the 25th Amendment to the Constitution, which ensures a clear line of authority and continuity in the executive branch.

In this situation, the Vice President steps in to fulfill the President's responsibilities and duties, ensuring that governmental functions continue without interruption. This provision is essential to maintain stability and public confidence during times of transition or crisis.

The other roles listed—Secretary of Defense, Speaker of the House, and Ambassador to the United Nations—do not have a constitutional basis for presidential succession. Each of these positions has its specific functions within the government, but they do not assume the presidency or its functions in the absence of the President.