Actually the black vote was perfectly republican until 1936, and then instantly switched to perfectly democrat that year, it is unique, they went from a pure GOP voting record to a pure dem voting record, instantly.
Jews have never gone republican, ever, in fact when given major candidates to the left of the dems (as in the 1920s), they flocked to them.
In 1920 while the democrat got 19% of their vote, the Socialist Party got 38% of it.
(There are plenty of Jewish Republicans however and we too are powerful and influential.)
Just which Republican presidential contender of the 1920s was "to the left of the dems?" Harding, Coolidge, or Hoover?