For the first time since the Cuban missile crisis in October 1962, top government leaders in Moscow are making explicit nuclear threats and officials in Washington are gaming out scenarios should President Vladimir Putin decide to use a tactical nuclear weapon to make up for the failings of Russian troops in Ukraine.

In a speech Friday, Putin raised the prospect anew, calling the United States and NATO enemies seeking Russia’s collapse and declaring again that he would use "all available means” to defend Russian territory — which he has now declared includes four provinces of eastern Ukraine.

Putin reminded the world of President Harry S. Truman’s decision to drop atomic weapons on Hiroshima and Nagasaki 77 years ago, adding, "By the way, they created a precedent.” On Saturday, the strongman leader of the southern Russian republic of Chechnya, Ramzan Kadyrov, said Putin should consider using "low-yield nuclear weapons” in Ukraine, becoming the first prominent Russian official to openly call for such a strike.