At noon on Friday, Jan. 20, the United States will have had three consecutive eight-year presidencies for only the second time in its history. The only other such moment came at noon, March 4, 1825, 192 years ago.

That’s a bit surprising, given George Washington’s example of retiring after two terms as president and the rule established by the 22nd Amendment, passed after Franklin Roosevelt won third and fourth terms in wartime, imposing a two-term limit. It owes something to the tragic happenstance that the four presidents who were assassinated might well have completed two terms otherwise.