Both the Democratic Party’s donkey and the Republican Party’s elephant symbols were popularized by satirical cartoons drawn by Thomas Nast from 1862 to 1886. The use of animal imagery was meant as a metaphor to compare American politics to a circus.
Nast’s use of the elephant for the Republicans dates to 1874 and a cartoon called “The Third Term Panic.” At the time, the New York Herald, a Democratic-leaning newspaper, was supporting rumors that Pres. Ulysses S. Grant might run for a third term in 1876. (It wasn’t illegal at the time but would have been unprecedented.) Nast portrayed the newspaper as a Democratic donkey trying to rile up other animals against the threat posed by the elephant that was the Republican Party.