For Trump and a section of the US right, breaking the nuclear taboo has always been thinkable. But doing so would teach China and Russia that it is morally and practically acceptable
In November 1950, when North Korean forces had the US military on the run, President Truman held an infamous press conference during which he threatened to declare nuclear war.
After a bland statement and several minutes of to and fro over diplomatic issues, one journalist asked whether the US was about to use its nuclear weapons. Truman stated not only that an attack was under active consideration but also that “the military commander in the field” would decide whether to hit military or civilian targets. He did not rule out attacking targets in China, either.