Presidential succession beyond the vice president
Presidential Succession Act - Wikipedia
https://en.wikipedia.org/wiki/Presidential_Succession_Act#Presidential_Succession_Act_of_1792Interregnum - Wikipedia
https://en.wikipedia.org/wiki/InterregnumPresident pro tempore of the United States Senate - Wikipedia
https://en.wikipedia.org/wiki/President_pro_tempore_of_the_United_States_SenateUnited States presidential inauguration - Wikipedia
https://en.wikipedia.org/wiki/United_States_presidential_inaugurationMillard Fillmore - Wikipedia
https://en.wikipedia.org/wiki/Millard_FillmoreZachary Taylor - Wikipedia
https://en.wikipedia.org/wiki/Zachary_TaylorTerm of office - Wikipedia
https://en.wikipedia.org/wiki/Term_of_officeDavid Rice Atchison - Wikipedia
https://en.wikipedia.org/wiki/David_Rice_AtchisonPresidential Succession Act - Wikipedia
https://en.wikipedia.org/wiki/Presidential_Succession_Act#Presidential_Succession_Act_of_1886Charles L. McNary - Wikipedia
https://en.wikipedia.org/wiki/Charles_L._McNaryWendell Willkie - Wikipedia
https://en.wikipedia.org/wiki/Wendell_Willkie1940 United States presidential election - Wikipedia
https://en.wikipedia.org/wiki/1940_United_States_presidential_election
Constitutional provisions
Twelfth Amendment to the United States Constitution - Wikipedia
https://en.wikipedia.org/wiki/Twelfth_Amendment_to_the_United_States_Constitution