get on the bandwagon

get on the bandwagon

To join or follow something once 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."
See also: bandwagon, get, on