Amid the continuing investigations into Russian meddling in the 2016 presidential election, there, of course, has been a great deal of discussion and news coverage of the 45th commander in chief not completing his full term in office.

If a sitting president leaves office, the vice president — currently Mike Pence — becomes president for the rest of the term. If he is unable to serve, the next person in the line of succession acts as president (see the chart below). To date, only a vice president has ever replaced the president.

The second in line, after Pence, is House Speaker Paul Ryan. And that oilman, who would follow Ryan and then Senate President Pro Tempore Orrin Hatch, into the West Wing? That would be Secretary of State Rex Tillerson.

American presidential succession laws date to 1792. The line of succession has been shuffled several times, including in 1868, when Congress removed the leaders of the Senate and House from the list, and, most recently, in 1967.

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