In 1994, not long after the nuclear crisis first flared with North Korea, President Bill Clinton considered launching an attack on the North’s main nuclear complex in Yongbyon north of Pyongyang, the capital, according to the South Korean president at the time, Kim Young-sam. Panic swept through South Korea, with people stocking up on food. Mr. Kim later said he had personally protested to Mr. Clinton, persuading Washington to drop the plan to strike Yongbyon.

After conducting five nuclear tests since 2006, North Korea is now widely believed to have several to as many as a dozen nuclear weapons, making a pre-emptive strike far riskier than it was in 1994. The North is also one of the world’s largest owners of chemical and biological weapons and apparently has no qualms in using them, as in the Feb. 13 assassination in Malaysia of Kim Jong-nam, the estranged half brother of the North Korean leader Kim Jong-un. Malaysia has said Kim Jong-nam was killed by the nerve agent VX.

Since Kim Jong-un took power five years ago, North Korea has conducted three nuclear tests and nearly 50 ballistic missile tests. And in his New Year’s Day speech, Mr. Kim said his country was in the “final stage” of preparing for its first test of an intercontinental ballistic missile.

Mr. Trump retorted at the time: “It won’t happen!”

Defense analysts said there were too many constraints for the United States to launch a pre-emptive strike against North Korea without expecting a major retaliation. North Korea keeps most of its crucial military assets in tunnels, and it remains unclear whether the United States and South Korean military planners have located them all. There are also 200,000 American civilians, as well as 28,500 United States troops, living in South Korea, and their neighborhoods would probably be among the first targets of any North Korean retaliation.

On Tuesday, North Korea’s main state-run newspaper, Rodong Sinmun, said that if the United States tried a pre-emptive strike, it would be “as foolish as putting its own neck on the chopping block.”

In another sign that North Korea has no intention of forsaking nuclear arms, top North Korean officials in Pyongyang gathered on Tuesday, the fifth anniversary of Mr. Kim’s election as leader of the ruling Workers’ Party, and vowed to uphold his policy of strengthening the North’s nuclear arsenal, the state news media reported. Also on Tuesday, Ri Su-yong, an 82-year-old Politburo member, former foreign minister, and adviser and childhood mentor to Mr. Kim, was given another powerful position in Parliament. Last year, Mr. Ri told Chinese officials that North Korea’s nuclear weapons expansion was “permanent.”

With less than one month left before the presidential election in the South, how to deal with North Korea has become a dominant campaign issue.