When Mrs. McG and I relocate out west, whoever is elected this November will either be well into his or her second-term slump, or will have been ejected from office the previous leap year by a mob carrying torches and pitchforks into the polling places (where poll workers won't be sure whether said implements constitute illegal electioneering).
In all seriousness, I can only think of one candidate still in the running today who has a chance of winning a second term. The alternatives would usher in another succession of one-termers, though probably not such as occupied the White House between Andrew Jackson's retirement in 1837 and Abraham Lincoln's re-election in 1864.
Jackson was the 7th president, Lincoln the 16th. In between, eight men held the presidency over the course of 24 years, the greatest presidential turnover in American history -- but inflated by the in-office deaths of William Harrison and Zachary Taylor. The presidents from Rutherford Hayes through William McKinley might have come close to matching the adjusted rate, except for Grover Cleveland's two non-consecutive terms and McKinley's 1900 re-election.
More recent high-turnover periods ran from 1960 to 1992, when seven men held the presidency over a period of 32 years. Lyndon Johnson, Richard Nixon and Ronald Reagan were re-elected during that period, but only Reagan served two full terms. Kennedy was assassinated, Nixon resigned; Ford, Carter and George H.W. Bush were all denied re-election.
How often have three consecutive presidents served two (or more) full terms, as Bill Clinton, George W. Bush and Barack Obama have (nearly) done? Jefferson, Madison and Monroe did it, as did Franklin Roosevelt, Truman and Eisenhower. And no one else. Three-peated eight-year presidencies are the exception in American politics. A four-peat would be unprecedented.
All this leaves me kind of looking forward to 2020. There have been times I've wanted to brandish a pitchfork at the polls, but I've never done it.