Joe Onek, The Hill
In the upcoming television series Designated Survivor, a massive terrorist attack elevates an obscure Cabinet Secretary to the Presidency. In real life, there is a far more likely and highly troubling presidential succession scenario.
Article II of the Constitution states that the Congress may by law provide “what Officer shall then act as President” when the President and Vice President are both unable to serve. In its most recent legislation on the subject, enacted in 1947, Congress provided that in such a situation the Speaker of the House shall succeed to the Presidency, followed by the President pro tempore of the Senate and then the Officers of the Cabinet ranked according to the dates their Departments were established – State, Treasury, Defense, etc.