jump on the bandwagon: align yourself with a popular cause, or what appears to be the winning side

In the nineteenth century, parades featured bandwagons -- heavy, horse-drawn wagons that carried brass bands along the parade route. The musicians inside sat in two facing rows as they played. The earliest example of the word in print comes from P. T. Barnum's 1854 autobiography: "we sold all our conveyances excepting four horses and the 'band wagon'."

The first non-musician to jump on the bandwagon may have been Zachary Taylor. During Taylor's 1848 presidential campaign, one of his strong supporters was a circus owner named Dan Rice. From time to time, Rice took Taylor up onto his bandwagon to ride around town, meeting and greeting the voters. Seeing the excellent publicity thus gained, other politicians vied to be taken up on a bandwagon also. Soon everyone running for office was jumping on his own personal bandwagon. The New York Evening Post for October 21, 1905 describes one such vehicle as having campaign posters pasted all over both sides.

By the 1920s bandwagons had disappeared, and people outside the world of politics were jumping on figurative bandwagons. Often these were enthusiastic supporters of some social or cultural trend. In recent times bandwagon has become a verb. We also have the "bandwagon effect," which is people's tendency to adopt a popular trend or support what they see as the winning side.

Read more about this expression in Let's Talk Turkey: The Stories Behind America's Favorite Expressions (Prometheus, June 2008).