Explanation: President Pro Tempore
The Constitution provides for a president pro tempore to preside over the Senate in the absence of the vice president. Except for the years from 1886 to 1947, the president pro tempore has been included in the presidential line of succession. Following passage of the Presidential Succession Act of 1792, the president pro tempore was next in line after the vice president, and followed by the Speaker of the House of Representatives. In 1886 a new law removed the president pro tempore and the Speaker from the line of succession, substituting cabinet officers. A 1947 law changed the order of succession to place the Speaker of the House in line after the vice president, followed by the president pro tempore, and then the secretary of state and other cabinet officers in order of their departments' creation. This is the system in effect today.
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