Bandwagon-jumper

The crowd was a mix of Little Leaguers and Wall Streeters, die-hard fans and bandwagon-jumpers.

Source: wiktionary

Populism is the new model of cool; elitists, rather than teeny-boppers or bandwagon-jumpers, are the new squares.

Source: wiktionary

Much as the tea party pushed rank-and-file Republican legislators toward positions once considered extreme, the resistance movement has already persuaded many Democratic elites to embrace the Sanders stance on issues such as Medicare for all, free college and government-guaranteed jobs. But the progressive movement, like the tea party, has no liking for bandwagon-jumpers.

Source: wiktionary