Thought these were some odd coincidences:
-Every President of the 20th century first elected in a year ending in 8 either lost re-election, declined to run, or served less than two elected terms.
1908: William H. Taft elected--Defeated in 1912
1928: Herbert Hoover elected--defeated in 1932
1948: Harry S. Truman elected, lost in the primaries and declined to run in 1952. He served nearly 4 years of FDR's term, but wasn't elected President in 1944; Thus, he did not complete two full elected terms.
1968: Richard M Nixon -- re-elected in 1972, but resigned in 1974, thus he did not complete two full elected terms.
1988: George H.W. Bush elected; he loses in 1992
Now in every year ending in 4 in the 20th and 21st century, the incumbent President won, and half of those incumbents were in office only due to the death of the President before them:
1904: Teddy Roosevelt elected; incumbent due to assassination of McKinley
1924: Calvin Coolige elected; incumbent due to death of President Harding
1944: FDR re-elected
1964: Lyndon Johnson elected; Incumbent due to the assassination of JFK.
1984: Ronald Reagan re-elected
2004: George W. Bush re-elected
Two years ending in 6 were won by narrow margins; two other years ending in 6 were landslides:
1916: Woodrow Wilson--Barely re-elected, getting only 49.2% of the popular vote
1936: Franklin Roosevelt re-elected in a landslide, winning 60.8% of the popular vote.
1956: Dwight D. Eisenhower re-elected in a landslide, winning 57.4% of the popular vote
1976: Jimmy Carter barely elected, warning 50.1% of the popular vote
1996: Bill Clinton barely re-elected, winning only 49.2% of the popular vote
Every President elected or re-elected in a year ending in 0 has either died in office, nearly died in office, or had a national catastrophe or embarrassment happen under their watch:
1900: McKinley re-elected; killed in the fall of 1901
1920: William G. Harding elected, dies in the Summer of 1923.
1940: FDR re-elected; Pearl Harbor occurs in the Winter of 1941; Dies Spring 1945
1960: JFK elected; Bay of Pigs fiasco in Spring 1961, killed in the Fall 1963
1980: Reagan elected; nearly killed in 1980; Beirut bombing in 1983.
2000: Bush elected, 9/11 occurs in the fall of 2001; Is nearly assassinated in Spring 2005.
Every President elected in a year ending in 2 in the 20th century won re-election:
1912: Woodrow Wilson elected; re-elected in 1916.
1932: FDR elected; re-elected in 1936
1952: Dwight Eisenhower elected; re-elected in 1956.
1972: Richard Nixon re-elected in 1972.
1992: Bill Clinton elected; wins re-election in 1996.