Collaborative governance has proliferated as a strategy to engage stakeholders in the complexity of environmental problems. However, collaboration has limitations, and increasing political polarization in many places could impact the ability to bring diverse stakeholders together. This research is a case study of collaboration in a public forest planning context facing social and political polarization in the American West. An alternate group formed, which reduced effectiveness of the collaboration and ultimately derailed the policy process. Using participant observation, semi-structured interviews, and document review, we identify trade-offs and discuss lessons that inform the design and implementation of collaborative governance regimes. We highlight the vulnerability of local collaboration to political shifts at other scales of government but also show how key collaboration dynamics related to facilitation, structure, representation, and shared learning interact with a polarized context to impact the trajectory of collaborative governance regimes.