South Korea has long been on the list of potential over-the-horizon proliferation challenges, but growing debates in Seoul about its nuclear options are quickly moving it toward the front of the U.S. nonproliferation agenda.

Yoon’s comments have fueled a debate in Washington over how to handle a problem that policymakers cannot wish away.

Although Russia’s war has created nuclear risks, the risk that it will unleash a wave of nuclear proliferation is lower than many believe.