Political Creatures: Why the Elephant and the Donkey?
Many sources credit Thomas Nast with the invention of the donkey as representing the Democratic party and the elephant representing the Republican party. Nast was a prominent caricaturist in the 1870s. His cartoon below from 1874 shows the donkey dressed in a lion's skin scaring all of the animals but the elephant, representing Republican voters.
The Donkey and Andrew Jackson
However representing the democrats with a "jackass" can be dated back to the 1920s and particularly the successful 1928 presidential campaign of Andrew Jackson. And Jackson decided to flip this obvious insult by openly adopting the donkey mascot as representing his strength ans stubbornness.
The Elephant has also been around for about a decade as a symbol employed to represent Republicans especially in a pro-Lincoln newsletter called "Father Abraham". The elephant was symbolic of battle and its connection to the party was then cemented by Nast's cartoons.
- Monaghan, J. (1944). Origin of Political Symbols. Journal of the Illinois State Historical Society (1908-1984), 205-212.