South Korea could become the next country to go nuclear. That’s the upshot of mounting calls in the South to develop its own nuclear deterrent in response to the North Korean strongman’s repeated threats to deploy “tactical nuclear warheads” against the South.

For years, rightist South Koreans — many of them aged Korean War veterans — have been saying South Korea needs its own nukes to counter the North in case Washington doesn’t come to the rescue. Now high-ranking conservatives in positions of power are joining the chorus.

The chairman of the emergency response committee of the ruling People Power Party, Chung Jin-suk, said “the time has come to make a decision” on jettisoning the joint agreement reached between the two Koreas 30 years ago, in which they pledged not to “test, manufacture, produce, receive, possess, store, deploy or use nuclear weapons.”

Having conducted its first nuclear test in 2006, North Korea has long since forgotten about the agreement. Now, Mr. Chung said the South should formally withdraw whenever Kim Jong-un orders the North’s seventh nuclear test. The dictator’s father, Kim Jong-il, ordered the North’s first two tests, and Mr. Kim has ordered four more nuclear tests, most recently in September 2017.

The South’s conservative president, Yoon Suk-yeol, strongly hinted that he was considering the nuclear option, saying he was weighing “diverse opinions across our nation and in the United States regarding extended deterrence” — a code phrase for the nuclear option.

Koreans are also asking if Washington might deploy nuclear warheads in South Korea for the first time since they were withdrawn at the behest of President George H.W Bush. The liberal who was then president of South Korea, Roh Moo-hyun, saw their withdrawal as essential while South and North Korea were negotiating their 1992 denuclearization agreement.

A major South Korean newspaper, JoongAng Ilbo, quoted a senior party member as saying South Korea plans to “begin discussions with the United States soon on ways to make the most of U.S. nuclear capabilities.” The official was quoted as saying “the core of the discussion is how effectively U.S. nuclear assets may be utilized in case of a contingency on the Korean Peninsula.”

The South Koreans, however, were under no illusions about the Biden administration responding with more than the usual assurances of defense of South Korea as a great treaty partner while focusing on the war in Ukraine.

Washington is not believed to see North Korea at this stage as going beyond Mr. Kim’s rhetorical flourishes while ordering tests of missiles supposedly capable of reaching targets anywhere in South Korea and Japan. If nuclear war were to break out, the Americans argue that Washington could respond with warheads on ships cruising the western Pacific and stored on air bases in Japan and Guam.

South Korea’s own nuclear program is another matter. A recent report by the Council on Foreign Relations says 70 percent of those polled favor South Korea developing its own nuclear weapons in view of uncertainty about the reliability of the American “nuclear umbrella.”