The evolution of U.S. nuclear policy and posture since the end of the Cold War -- The first new problem : nuclear-armed regional challengers -- The new regional deterrence strategy -- The second new problem : relations with Putin's Russia -- The evolving relationship with China -- Extended deterrence and strategic stability in Europe -- Extended deterrence and strategic stability in Northeast Asia -- The broader nuclear assurance agenda -- Conclusions -- Epilogue : implications for future strategy, policy, and posture reviews.