“The end of arms control as we know it”

The last agreement limiting America’s and Russia’s nuclear arsenals is months away from expiring.

In December 2019, a secretive group of elite Americans and Russians gathered around a large square table. It was chilly outside, as Dayton, Ohio, can get in the winter, but the mood inside was just as frosty.

The 147th meeting of the Dartmouth Conference, a biannual gathering of citizens from both nations to improve ties between Washington and Moscow, had convened. Former ambassadors and military generals, journalists, business leaders, and other experts came together to discuss...