South Korean conservatives are counting on the return of Donald Trump to the White House slightly more than two months from now to add urgency to demands for the South to produce its own nukes in response to the fast-rising threat from the world’s ninth nuclear nation, North Korea.

“They already have a wide body of support,” said the Center for Strategic and International Studies’ Victor Cha. “It’s worrying.”

Mr. Cha is author of a lengthy CSIS report, “Breaking Bad: South Korea’s Nuclear Option.” During a Korea Society meeting at New York last week, Mr. Cha said the threat from the People’s Republic of China and Russia, united in their support of the North, adds to the South’s “many reasons for having nuclear weapons.”

Mr. Cha, who served as northeast Asia expert on the national security council during the George W. Bush presidency, says the South’s President Yoon again stuck to his view that Seoul can count on Washington to rush to its defense in a nuclear war.

For North Korea “to decide to wage a nuclear attack” against South Korea would be “irrational,” Mr. Yoon said in a Newsweek interview that was widely quoted in South Korea. “Should they do so,” he said, the Korean-American alliance “will immediately strike North Korea with U.S. nuclear weapons.”

The prospect of a second Trump presidency, however, fuels fears in the South that Washington will sharply decrease its support for the alliance as Trump threatened during his first presidency. Trump upset South Korean leaders by raising the possibility of withdrawing some if not all of America’s 28,500 troops from South Korea if Seoul did not meet his demands for a vast increase in the amount the Americans are paid for defending the South.

Worry about Trump’s support of Nato reverberates in South Korea while North Korea arms the Russians not only with weapons but also with North Korean troops for the war in Ukraine. It was Trump, Mr. Cha noted, who said the Russians “can do whatever the hell they want” to Nato countries that didn’t pay their share for defense of Europe including the war in Ukraine — a remark that he might apply to South Korea too.

“I would suspect there’s a lot of thinking going on right now, like, what’s next,” said Mr. Cha, talking about behind-the-scenes debate in ruling circles in Seoul. “What’s next is very much dependent on what the U.S. does. If we hear things that sound like decoupling, that’s going to trigger things in South Korea.”

The landmark CSIS study on attitudes in South Korea on going nuclear cited “increasingly open discussion” in the South “about the previously taboo topic of national nuclear weapons capability.” The study found that polling showed “over 76 percent of South Koreans” in favor of “a nuclear path” — meaning either the South should develop its own nukes or the return of American nukes, withdrawn by President George W. Bush from foreign soil, including South Korea, in 1991.

The CSIS poll of more than 1,000 “strategic elites” in South Korea showed that two thirds of them did not favor the South going nuclear — a figure that contrasted with the high percentage of the general public that wanted the South to get its own nukes.

“The main reason South Korea’s strategic elites do not favor nuclearization is the consequences in terms of international condemnation, reputational costs, and sanctions,” said the CSIS study, but circumstances could change rapidly. 

“Should abandonment fears regarding the U.S. security commitment come to fruition such as the withdrawal of U.S. ground troops by a future U.S. administration,” it said, “51 percent of those opposed to nuclearization would become supportive.”

For South Korea to go nuclear, Mr. Cha noted, would raise huge problems with China and Russia, two nuclear powers that would respond with alarm to a nuclear South Koreas. Both of them have shown their full support for the North by vetoing numerous UN Security Council resolutions calling for increased sanctions. 

“The most secure thing for Korea going forward is the alliance” with Washington, said Mr. Cha. That’s “the safest, most cost-effective way to go,” — while “none of our global institutions are working,” notably the UN.