I heard this one when Reagan was elected: "William Henry Harrison was the first President to die in office. He was elected in 1840. Since then, every President elected in a year ending in 0 has died in office."
And then ...
... Reagan didn't die. And 0 was still a "numerical constant."
Reagan was the first to break that rule.... Lincoln, elected 1860, was assassinated in 1865. Arthur Garfield, elected 1880, was assassinated in 1881. William McKinley, elected in 1900, was assassinated in 1901. Warren G. Harding, elected in 1920, died in office in 1923. FDR, elected in 1940, died in office in 1945. John F. Kennedy, elected in 1960, assassinated in 1963. Ronald Reagan, elected in 1980, narrowly escaped assassination in 1981. George Bush is the second President elected in a year ending in “0” not to die in office.