Amendment 25

"Section 1. In case of the removal of the President from office or of his death or resignation, the Vice President shall become President.

Section 2. Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.

Section 3. Whenever the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that he is unable to discharge the powers and duties of his office, and until he transmits to them a written declaration to the contrary, such powers and duties shall be discharged by the Vice President as Acting President.

Section 4.Whenever the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of the office as Acting President. Thereafter, when the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that no inability exists, he shall resume the powers and duties of his office unless the Vice President and a majority of either the principal officers of the executive department or of such other body as Congress may by law provide, transmit within four days to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office. Thereupon Congress shall decide the issue, assembling within forty-eight hours for that purpose if not in session. If the Congress, within twenty-one days after receipt of the latter written declaration, or, if Congress is not in session, within twenty-one days after Congress is required to assemble, determines by two-thirds vote of both Houses that the President is unable to discharge the powers and duties of his office, the Vice President shall continue to discharge the same as Acting President; otherwise, the President shall resume the powers and duties of his office."

In the 25th amendment, it outlines the process of impeaching the President and how the VP will take command if the President dies. There have only been a few circumstances in history where either of these events occurred. This amendment also states that the President can resign if he believes he is not fit for his duties. 

In this video, Hughes discusses the process of the 25th amendment. He also explains how we came up with the Vice President taking over if the President dies or resigns. The "Tyler Precedent" states that the VP will be the acting President if the current President dies/resigns. This happened because of William Henry Harrison after he died, his VP John Tyler sort of took over, but Congress had to pass a resolution for him to the the acting President. 

Pictured above is the moment Lyndon B. Johnson was sworn in as President on Air Force One, after John F. Kennedy was killed. Jackie Kennedy is on the right in the photo, as you can see all people in the picture are in disbelief. This is, unfortunately, an iconic moment; anyone in or from the U. S. would know this picture and could tell you who these people are.