But it wasn’t just overegged fear of Mr. Putin’s nukes. The Biden and Trump administrations recognize the many ways Mr. Putin can make their lives difficult: cyberattacks, assassinations, sabotage, threats to undersea cables and now satellites. Russia can peddle ICBM technology to North Korea, submarine technology to China, antiship missiles to Iran, etc.

Willing the ends without willing the means is the happy prerogative of the pundit through the ages.

But no principle is advanced by making the perfect the enemy of the good. The reality principle defines every armistice ever concluded, including the many ugly ones you’re already thinking of.

Mr. Trump has a reputation for bold moves only in a relative sense: Politics makes all politicians risk-averse. They prefer small, reversible steps. They kick the can down the road whenever possible.