CuttleMemes

The term "bandwagon effect" is thought to have originated in the 19th century, when it was used to describe the practice of politicians who would literally ride on a bandwagon as part of their campaign, in order to attract attention and supporters. 

The phrase "jump on the bandwagon" first appeared in American politics in 1848 during the presidential campaign of Zachary Taylor (the 12th President of the United States of America, serving from 1849  1850). 

Dan Rice (1823  1900) was a famous circus clown and entertainer of the time, who invited Taylor to join his circus bandwagon  literally to campaign for the presidency while on top of his circus bandwagon. 
As Taylor gained more recognition (due to the increased visibility and therefore distribution of his memes), his campaign became more successful. 

People began saying that Taylor's political opponents ought to "jump on the bandwagon" themselves if they want to be associated with such success.

Later, during the time of the William Jennings Bryan's 1900 presidential campaign, bandwagons had become standard in campaigns (Taylors strategy for meme distribution was copied), and the phrase "jump on the bandwagon" was used as a derogatory term, implying that people were associating themselves with success without considering that with which they associated themselves.

Today, the Bandwagon Effect refers to the psychological phenomenon whereby the rate of uptake of memes (beliefs, ideas, fads and trends) increases with respect to the proportion of the size of the network of meme propagators.

In other words, as more people come to believe in something, others also "hop on the bandwagon" regardless of the underlying evidence.

This image was co-created with DALLE 2, and depicts politicians atop a bandwagon, increasing their visibility, and therefore the distribution of their memes to the masses.