on the bandwagon, get

To join, follow, or support someone or something only after it is successful or popular. I can't stand these people who just get on the bandwagon after a win. Where were they last year when the team was terrible? A: "I thought your mom hated that candidate." B: "Well, he's the president now, so she decided to get on the bandwagon."

Also, climb or hop or jump on the bandwagon . Join a cause or movement, as in More and more people are getting on the bandwagon to denounce cigarette smoking. This expression alludes to a horse-drawn wagon carrying a brass band, used to accompany candidates on campaign tours in the second half of the 1800s. By about 1900 it was extended to supporting a campaign or other cause.