The original Presidenial Succession ACt of 1792 had placed the Senate president pro tempore and Speaker of the House in the line of succession, but in 1886 Congress had removed them.
In 1886, Congress passed a new Presidential Succession Act, making the Secretary of State next in line after the Vice President.
In 1945, President Truman requested that the law be changed. He suggested putting the Speaker of the House and then the Senate President pro tempore ahead of the Secretary of State.
https://www.senate.gov/artandhistory/history/minute/Presidential_Succession_Act.htmEdited by Spanky at 15:53:34 on 01/08/20