POTUS incumbency is very powerful in re-election bids

The 2020 Presidential Election is #59 and there have been 9 incumbent losses.

(9) George H.W. Bush lost to Bill Clinton in 1992. (Ross Perot took 19% of vote)
(8) Jimmy Carter lost to Ronald Reagan in 1980. (intra-party challenge by Ted Kennedy)
(7) Gerald Ford lost to Jimmy Carter in 1976. (Geral Ford never elected Pres. or Vice Pres.)
(6) Herbert Hoover lost to Franklin D. Roosevelt in 1932. (President at start of depression )
(5) William Taft lost to Woodrow Wilson in 1912. (Teddy Roosevelt took 27% of vote)
(4) Benjamin Harris lost re-election in 1892 to former President Grover Cleveland.
(3) Grover Cleveland lost a re-election bid in 1888, but won his re-election in 1892,
(2) Martin Van Burn lost a re-election bid in 1840
(1) John Adams lost his re-election bid in 1800 to Thomas Jefferson (the only founding father to not be re-elected)

Former Presidents (who were not incumbents) who ran in a third party and lost the election
(1) Millard Filmore was elected VP in 1848, became POTUS when Zachary Taylor got dysentary. MF served out the remainder of his turn, did not run in 1852, and ran as a third party candidate in 1856 when he lost.
(2) Teddy Roosevelt was elected VP in 1900, became POTUS when William McKinley was shot TR served out the remainder of his turn, was elected in 1904, and ran as a third party candidate in 1912 when he lost.

In contrast, there were 21 incumbent Presidents who won re-election, and FDR won four elections.