Do electoral politics influence nuclear strategy and treaty negotiations? After a hotly contested debate around the New START Treaty in 2010, President Barack Obama scheduled a ratification vote following the November midterm elections, during the lame duck session. The timing of the vote provided enough political cover for a few moderate Republicans to break ranks and ratify the treaty by just four votes. Conventional wisdom describes the politics surrounding New START as both an outlier and function of partisanship within the U.S. Senate. However, the opposition to New START was neither unique nor fully explained by ideology. Using historical evidence and data on Senate ideal points, this article shows that polarization and electoral politics drive partisan opposition to arms control and most fully explain opposition to New START. Continued trends toward polarization and party sorting may have dramatic and unforeseen consequences for the future of U.S. foreign policy outcomes.