We investigated the dynamics of identity fusion and prosocial behavior within political groups in the four weeks preceding and following the 2016 U.S. Presidential Election. The primary questions were whether a negative event (losing) would lead to a more pronounced increase in identity fusion, and whether identity fusion would predict prosocial giving. We found that while fusion gradually increased in the run-up to the election, there was no significant increase after the event for supporters of either party. We also found that identity fusion robustly predicted prosocial ingroup giving, especially before the election, and even when accounting for self-reported identification and previous political commitment behaviors. Implications for theories of identity fusion are discussed.