NATO agrees to missile-defense mission. Somewhat paradoxically, this is true even if you’re lukewarm on ballistic missile defenses (BMD) in general, or the Phased Adaptive Approach in particular. Why? The more NATO presents a united front, the more likely the Russians are to cooperate on BMD and BMD-related issues, which not only reduces an irritant in relations but mitigates against some of the potentially destabilizing implications of BMD deployment.
Afterthought: might also help with New START ratification. Harder to argue that Obama is selling out BMD when he’s accomplished something no Republican ever did: convince NATO to make it part of its mission.