Why it matters: The 2010 treaty is the last remaining constraint on the arsenals of the world’s two nuclear superpowers, limiting the number of deployed nuclear warheads and the bombers, missiles and submarines which can deliver them.

Russia has already expressed support for five-year extension — a simple process that only requires an exchange of diplomatic notes.

Biden has long supported an extension, but his administration hadn’t previously committed to the five-year timeframe.

The other side: The Trump administration was skeptical of New START, arguing that it had allowed Russia to build up advanced nuclear systems that aren’t constrained by the treaty.