The field of journalism is experiencing intense diversification in form and message while trying to overcome widespread public disaffection by reinforcing professional norms. This study focuses on two forces-normalization and fragmentation-by observing them at work on social media. We analyzed content and interactions from mainstream and non-mainstream political journalists covering a 2016 U.S. presidential debate. Forces of normalization would draw these two groups of reporters together in a monolithic, widespread practice, perhaps including both newer and older methods. Forces of fragmentation, on the other hand, would drive groups of practitioners further apart, with clearer lines separating mainstream journalism from its offshoots. The key question is where these similarities and differences between mainstream and non-mainstream journalists arise. Findings suggest divergence in objectivity and gatekeeping, and convergence in campaign coverage practices. The evidence suggests that, on Twitter, mainstream reporters insulate themselves by interacting mainly with other journalists, while nonmainstream journalists offer openly partisan interpretations and seek out audience participation and engagement, often from people sharing their viewpoints.