It’s unclear how long it’ll take to negotiate a New START Treaty, and waiting too long, allowing the current treaty to lapse, or signaling that the U.S. isn’t committed to New START could be disastrous for the global nuclear order. Perceived lack of American commitment to START could also embolden Russian military adventurism, risking more situations like Crimea.
Since the New START Treaty took effect in 2011, Russia has developed new nuclear weapons that aren’t covered by it and adopted an aggressive nukes-first military policy that needs containment. Both of these issues need to be addressed in a new treaty that has more enforcement authority to verifiably reduce Russia’s nuclear weapons stockpile.