Who is the third in line should both the President and the VP become incapacitated during a term?
The Speaker of the House is the presiding officer of the chamber. The office was established in 1789 by Article I, Section 2 of the United States Constitution, which states in part, "The House of Representatives shall choose their Speaker..." The Constitution does not require that the Speaker be an elected House Representative, though all Speakers have been an elected Member of Congress.
The Speaker is third in the United States presidential line of succession, after the President and the Vice President and ahead of the President pro tempore of the U.S. Senate. Unlike some Westminster system parliaments, in which the office of Speaker is considered non-partisan, in the United States, the Speaker of the House is a leadership position and the office-holder actively works to set the majority party's legislative agenda. The Speaker usually does not personally preside over debates, instead delegating the duty to members of the House from the majority party. The Speaker usually does not participate in debate and rarely votes.