20 Presidents or former Presidents have been elected to a second term.
But 10 have not.
Which, abstractly, gives Trump a 1/3 chance of losing (i.e. nothing is certain; cf. Gerry Ford, Jimmy Carter or GHW Bush)
10 Presidents who ran unsuccessfully for a second term in the same party (half in the 18th-19th centuries; half in the 20th):
1800 John Adams
1832 John Quncy Adams
1840 Martin Van Buren
1888 Grover Cleveland (won popular vote but not Electoral College)
1892 Benjamin Harrison
1912 Wm Howard Taft
1932 Herbert Hoover
1976 Gerald Ford (never elected President or VP)
1980 Jimmy Carter
1992 Geo. H.W. Bush
3 Former Presidents who ran unsuccessfully for another (non-consecutive) term under a different party label:
1848 Martin Van Buren (Free Soil, elected 1836 and lost 1840 as a Democrat)
1856 Millard Fillmore (American/Whig, served 1850-53 as Whig VP succeeding Zachary Taylor, lost Whig nomination in 1852)
1912 Theodore Roosevelt (Progressive, served 1901-5 as McKinley’s successor, elected in own right in 1904 and announced in 1906 that he wouldn’t seek a 3rd term, all as a Republican)
20 Presidents who won a second term:
1792 Washington
—— (1800 J. Adams lost)
1804 Jefferson
1812 Madison
1820 Monroe
—— (1828 J.Q, Adams lost)
1832 Jackson
—— (1840 Van Buren lost)
1864 Lincoln
1872 Grant
—— (1888 Cleveland, incumbent, lost Electoral vote while winning a popular plurality)
—— (1892 Benjamin Harrison lost)
1892 Cleveland (only non-consecutive 2nd term)
1900 McKinley
1904 Theodore Roosevelt (elected as VP in 1900, succeeded McKinley in 1901)
—— (1912 Taft lost)
1916 Wilson
1924 Coolidge (elected as VP in 1920, succeeded Harding in 1923)
—— (1932 Hoover lost)
1936, 1940 & 1944 FDR
1948 Harry Truman (elected as VP in 1944, succeeded FDR in 1945)
1956 Eisenhower
1964 LBJ (elected as VP in 1960, succeeded JFK in 1963)
1972 Nixon
—— (1976 Ford lost)
—— (1980 Carter lost)
1984 Reagan
—— (1992 Geo. H.W. Bush lost)
1996 Clinton
2004 GW Bush
2012 Obama
¶ Some day. no doubt, you’ll thank me.
Dave