Meaning

noun the symbol of the Democratic Party; introduced in cartoons by Thomas Nast in 1874

noun domestic beast of burden descended from the African wild ass; patient but stubborn

originFrom the fact that a donkey is typically depicted as a clumsy animal with a lack of intelligence (evident in terms such as ass and donkey vote), in comparison to a horse which is depicted as a strong and powerful companion animal. A bronco is a bucking horse.

Etymology from Wiktionary, CC BY-SA 3.0