A plurality of presidents have only served one term; serving two full terms is less likely than you would think. Over the past 232 years we’ve seen 45 presidencies, which averages to 5.1556 years each, so just over one term (if we only count Grover Cleveland once, then it goes up to 5.2727 years)
Washington (8)
Adams (4)
Jefferson (8)
Madison (8)
Monroe (8)
Adams (4)
Jackson (8)
Van Buren (4)
Harrison (~0; died of pneumonia after 1 month)
Tyler (~4; completed Harrison’s term)
Polk (4)
Taylor (~1; died of a stomach ache)
Fillmore (~3; completed Taylor’s term)
Pierce (4)
Buchanan (4)
Lincoln (~4; re-elected, assassinated)
Johnson (~4; completed Lincoln’s second term)
Grant (8)
Hayes (4)
Garfield (~0; assassinated)
Arthur (~4; completed Garfield’s term)
Cleveland (4)
Harrison (4)
Cleveland again (4 (8 total))
McKinley (~4; re-elected, assassinated)
Roosevelt (~8; completed McKinley’s second term, re-elected)
Taft (4)
Wilson (8)
Harding (~2; died of a heart attack)
Coolidge (~6; completed Harding’s term, re-elected)
Hoover (4)
Roosevelt (~12; three full terms, died of a brain hemorrhage in fourth)
Truman (~8; completed Roosevelt’s fourth term, re-elected)
Eisenhower (8)
Kennedy (~2; assassinated)
Johnson (~6; completed Kennedy’s term, re-elected)
Nixon (~5; re-elected, resigned)
Ford (~3; completed Nixon’s second term)
Carter (4)
Reagan (8)
Bush (4)
Clinton (8)
Bush (8)
Obama (8)
Trump (4)
Biden (ongoing)
We’ve never had a run of four two-termers in a row, and we’ve never made it more than eight presidencies without an irregular transition; we’re overdue, if you’re superstitious.
Adams 2 and 6 were father and son.
Harrison 9 and 23 were grandfather and grandson.
Johnson 17 and 36 were unrelated.
Roosevelt 26 and 32 were fifth cousins once removed.
Bush 41 and 43 were father and son.
Of the 45 individuals elected president, 8 have been related; that’s 17.8% If Kennedy’s brother Bobby hadn’t been assassinated, he may have become president too. Hillary Clinton came close, and Trump’s spawn are almost certainly gonna run in the future.  It’s a nepotism machine.
