There is an air of desperation around Ukrainian President Volodymyr Zelensky these days as he tries to convince his Western allies, the United States in particular, that he has a realistic plan to force Russian President Vladimir Putin to give up his maximalist goals and sue for peace.

The Kremlin has had little success invoking its nuclear arsenal to deter Ukraine and the West from using new tactics to stop Russia’s invasion. That may be changing.

A close ally of President Vladimir Putin warned Western governments on Thursday that a nuclear war would ensue if they gave the green light for Ukraine to use long-range Western weapons to strike targets deep inside Russia.