All that nuclear talk: Is the unthinkable suddenly possible?

First, Vladimir Putin raised the prospect of using nuclear weapons to further his aims in the war in Ukraine.

Then North Korea’s Kim Jong Un followed suit, announcing his field inspection of tactical nuclear weapons units. That seemed to confirm a change in nuclear weapons strategy Mr. Kim had hinted at earlier this year – from “no first use” to foreseeing the use of battlefield tactical nuclear weapons.

To many experts, the sudden crescendo in talk of nuclear weapons suggests an epochal shift in perception of the use of nuclear...