Yep it is rare.
While candidates who lost in the primaries frequently come back and run for president again, it’s rare for someone who got the nomination and lost the general election, to ever run for president again.
In recent history, Stevenson in 1952 and 1956, and Nixon in 1960 and 1968 are the only ones I can think of offhand.
Consider others. Goldwater lost in 1964, never ran again. Humphrey in ‘68, ran again in the ‘72 primaries but did not get the Democrat nomination again. Ford in ‘76, Carter in 1980, Mondale in 1984, Dukakis in 1988, Bush 41 in 1992, Dole in 1996, Gore in 2000, Kerry in 2004, McCain in 2008, Romney in 2012 -— all lost the general election, and never ran for president again.
So Hillary is up against some tough history, if she thinks she can waltz to the nomination just because she was top dog for the Democrats and considered “inevitable” before.
Her biggest obstacle is left-wing Democrats despise her. They won’t vote for her.
And they haven’t forgiven her for swindling them out of Bernie.
And without them, she can’t win an election.
There seems to be a strong sentiment among the Democrat rank and file that they have had enough of Hillary. Many, many of those who supported her and voted for her want her to go away. And then you have the Bernie brigade. No way she gets the nomination (unfortunately!).
William Jennings Bryan ran in 1896, 1900, and 1908 and lost all three times first to McKinley and then to Taft. Clinton should run again, she would be following a tradition started by Bryan.