No two-term limit or tradition-Grant very likely wins third term 1876, maybe even fourth one.TR carries on in 1908, maybe even 1912 and 1916-wins WW1 earlier,dies in office. Vice-president-Hiram Johnson or William Howard Taft.
1960-Eisenhower wins third term -Kennedy doesn't challenge him. 1964-JFK elected over Nixon. 1968-JFK rather than Bobby assassinated. President Johnson already announce stepping down-Nixon wins. 1976-Bobby President. 1980-loses to Reagan. Same until 200-Bill Clinton could have won third term-at least. So,later could Barack Obama.