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 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.
Okay, here is the actual superseding of the President of the United States to include his removal from office by the Congress and Vice President if for any reason he is incapacitated. This is very similar to the relieving of command by subordinates of a superior officer who is in conflict with mission or objectives. The most perfect example of this is when Regan was shot no one really knew who was in charge of the Presidents office, thus an particular set of rules and orders were put into place to prevent the vacancy of the Presidents office.
Realistic Movie about what Could Happen!!
This is the movie Dave in which a normal guy who looks like the President is employed as such due to the real president being incapacitated. Although a normal civilian would never really be able to do this the idea that the government would use tactics like this is nothing new or to be underestimated. The government uses look alike all the time for particular events and engagements without the public even knowing.
An Actual use of a Look Alike, although Funny actually possible
This is a hilarious example of how the president and a look alike are similar in action and mannerisms and can be used in lieu of the supercedance clause of the amendment. Although this could be used to bar the president returning to office, especially if both the president and vice president are out of commission.