Andrew Jackson was considered a jackass in his 1828 election and labeled as such by his opponents. Jackson ran with it and used the jackass as a symbol in his campaign. This did not stick as a Democrat mascot until cartoonist Thomas Nast published a cartoon in Harper's Weekly in 1870. The public loved it and it took off. Harper's Weekly was popular. In 1874, Nast issued another cartoon with an elephant as a Republican and then we had both mascots as both were now accepted by the general public. It's all media.