 And then it says this, 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, listen to this, 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 VP shall immediately assume. So let's say the president had, God forbid, a massive stroke.