The politics of nuclear arms control between the United States and Russia are in a protracted state of crisis, which is in need of explanation. This article provides an overview of bilateral contractual milestones from 1972 to 2001 and analyzes instances of cooperation through the lens of three key factors that have influenced the process. It then considers the changes that these factors have undergone over twenty years of crisis in bilateral arms control from 2001 to 2021 and gauges the possible consequences of a continuation of the current situation. It concludes that during the first period, a shared willingness to shield the bilateral process from political disruption, U.S. bipartisan support, and cooperatively addressing the vertical diffusion of offensive and defensive missile capabilities were both possible and necessary for ensuring success. During the second period, these key factors underwent significant changes and ultimately had a negative effect on the bilateral process, which makes the current crisis unique compared to earlier episodes of regression. Most importantly, both sides were no longer willing to shield the bilateral process in its entirety during this period, including defensive and sub-strategic offensive elements. With a view to future consequences, these findings point to reduced arms race stability, weaker negotiated outcomes, and an erosion of the global nonproliferation regime.