Although political action often requires activists to express who they are and what they stand for, little is known about the motivators of such identity expression. This research investigates how group identity content and identification with this content predict identity-expressive collective action in the U.S. 2016 presidential elections. We recruited a longitudinal community sample of U.S. party supporters ( N = 426) mid-October (T1), beginning November (T2), and mid-November (T3). Participants listed words they associated with party campaigners, and self-reported their identification with this identity content and the politicized group. Supporting H1, politicized group identification longitudinally predicted increased frequency of collective action more strongly than did identification with specific identity content. Supporting H2, identification with specific identity content longitudinally predicted increased desires to express that content through collective action more strongly than politicized group identification. Implications for our understanding of identity expression and identity content in collective action are discussed.