How do we understand political polarization around the issue of climate change in the United States? Using a mixed-methods approach, this paper unpacks the components of the debate over climate science and policy between 2015 and 2017 to understand the sources of divisiveness that have come to characterize climate politics in the United States. Data in our analysis include the content of Congressional hearings and open-ended, semi-structured interviews with the most influential climate policy actors at the federal level. We find high levels of polarization around two specific components of this debate: the type of policy instrument and the role of the federal government in regulating carbon dioxide emissions. This paper concludes by exploring how patterns of polarization preceding the 2016 election help us to understand the expected political debate over federal climate policy in the years to come.