Jump on the bandwagon
Join a growing movement in support of someone or something, often in an opportunist way, when that movement is seen to have become successful.
The word bandwagon was coined in the USA in the mid 19th century, simply as the name for the wagon that carried a circus band. Phineas T. Barnum, the great showman and circus owner, used the term in 1855 in his unambiguously named autobiography The Life of P.T. Barnum, Written by Himself, 1855:
"At Vicksburg we sold all our land conveyances excepting four horses and the 'band wagon'."
Barnum didn't coin 'jump on the bandwagon', which came later, but he did have a hand in some other additions to the language. He was nothing if not a publicist and, even though there is no definitive evidence of his inventing any new word or phrase, he certainly can be said to have made several of them popular. Firstly, there are a couple of celebrated quotations:
"There's a sucker born every minute." and
"You may fool all the people some of the time; you can even fool some of the people all the time; but you can't fool all of the people all the time."
The Oxford Dictionary of Quotations lists those under their Barnum entry, along with the dictionary compiler's favourite weasel words - "attributed to". There is considerable doubt that he said either of the above. Barnum's acquaintances have claimed that the first would have been somewhat out of character for him, and Abraham Lincoln is often confidently cited as the author of the second. Actually, the 'some of the people' dictum isn't found in print until 1887 (some years after Lincoln's death and when Barnum was in his dotage), when it appears in print in several American newspapers, again guarded by vagaries like "Lincoln once said".
Two other terms that we certainly can thank Barnum for popularising are 'Jumbo' and 'Siamese twins'. Jumbo was a little-used slang term in Barnum's day and was recorded in John Badcock's Slang. A dictionary of the turf, 1823:
"Jumbo, a clumsy or unwieldly fellow."
The word was coined as the the name of a giant elephant that was housed at London Zoo. Jumbo was sold to Barnum in 1882 and exhibited in his shows. It is via Barnum's marketing zeal that the word became widely used as epitomising hugeness. The creature itself didn't have much luck. It died in 1885 after being struck by a train. Its heart was cut out and the torso was stuffed and mounted and continued to tour with Barnum's circus. It was destroyed in a fire in 1975 and now languishes as 14 ounces of ash in a peanut butter jar.
Barnum's other contribution to the language is the term 'Siamese twins', which he applied to the 'joined at the hip' brothers Chang and Eng Bunker.
Back to the bandwagon. Circus workers were skilled at attracting the public with the razzmatazz of a parade through town, complete with highly decorated bandwagons. In the late 19th century, politicians picked up on this form of attracting a crowd and began using bandwagons when campaigning for office.
The transition from the literal 'jumping on a bandwagon', in order to show one's alliance to a politician, to the figurative use we know now was complete by the 1890s. Theodore (Teddy) Roosevelt made a clear-cut reference to the practice in his Letters, 1899 (published 1951):
"When I once became sure of one majority they tumbled over each other to get aboard the band wagon."
See other phrases that were coined in the USA.