South Korea’s president, Yoon Suk-yeol, sees his visit to Washington as the triumphant beginning of a brave new era in the confrontation with North Korea.

Back at Seoul, Mr. Yoon is telling skeptical Koreans his summit with President Biden “allows our future generations to nurture their dreams at ease.” As evidence, he is citing the Washington Declaration, the document signed by the two presidents, as guaranteeing “a South Korean model of extended deterrence” — a phrase that implies much strengthened defense against the North.

By way of contrast, Mr. Yoon compared his approach with that of his liberal predecessor, Moon Jae-in, who spurned military exercises with the Americans while pursuing dialogue with the North Korean leader, Kim Jong-un. As reported by South Korea’s Yonhap News, Mr. Yoon said he was seeking “peace by overwhelming power, not a fake peace that relies on the other side’s good will.”

It would be premature, though, to expect real change in the state of play between the two Koreas. True, Mr. Yoon pressed all the right buttons in the well-choreographed summit, during the soiree in which he sang a verse from “American Pie” at the urging of his host, Mr. Biden, and in his address to both houses of Congress beginning with the sacrifices of Americans as well as Koreans in the Korean War.

After all’s said and done, though, the response from North Korea suggests we can now look forward to what we’ve been seeing and hearing all along from the North.

“The United States and the south Korean puppets make desperate efforts to suffocate” the North, a commentary put out by Pyongyang’s Korean Central News Agency said, referring to the South with a lowercase “s.” “Their dangerous nuclear war moves can never be pardoned but shall be paid dearly.”

It was up to Kim Jong-un’s younger sister, Kim Yo-jong, to brandish the nuclear threat. “The pipe dream of the U.S. and south Korea will henceforth be faced with the entity of more powerful strength,” Yo-jong, who periodically makes statements that are markedly more colorful than her brother’s harangues, said.

The North’s “nuclear war deterrent” should be “brought to further perfection,” she warned. “The more the enemies are dead set on staging nuclear war exercises, and the more nuclear assets they deploy in the vicinity of the Korean peninsula, the stronger the exercise of our right to self-defense.”

That kind of rhetoric, on top of scores of North Korean missile tests, explains the rising pressure within South Korea to make its own nuclear weapons and for Washington to plant American nukes in South Korea, from which President George H.W. Bush withdrew them in 1991.

On these critical points, though, the Koreans are resigning themselves to the reality that South Korea must rely as always on the American nuclear umbrella. The Americans may have assured the Koreans of “extended deterrence,” but the basic impression was, the more things change, the more they stay the same.

“It seems the United States is more concerned about South Korea’s nuclear development than about neutralizing North Korea’s nuclear weapons,” the conservative Chosun Ilbo, South Korea’s biggest-selling newspaper, wrote in an editorial. “The question remains whether Washington will really protect Seoul even if that places U.S. territory in the crosshairs of North Korea’s nuclear missiles.” 

Mr. Yoon sought to allay such criticism as he discussed  the outcome of the summit with his cabinet.

“It’s important to properly flesh out the Washington Declaration in the process of information sharing, joint planning and joint execution with respect to the operation of U.S. nuclear assets,” Yonhap quoted him as saying. America’s “powerful strategic assets,” he said, “will be regularly deployed near South Korea, allowing it to maintain an “overwhelming punishment posture.”

He said the Nuclear Consultative Group announced at the summit would be “more effective than NATO’s Nuclear Planning Group in that South Korea and the U.S. will have discussions more frequently and more deeply on a one-on-one basis.” 

A long-time Korea analyst with the RAND Corporation, Bruce Bennett, demurred. “The Washington Declaration is burdened with the typical U.S. over-use of strategic ambiguity,“ he told the Sun. “What is the function of the Nuclear Consultative Group? Will it establish nuclear targeting guidelines for use in the Korean theater in a manner similar to what Robert McNamara as Secretary of Defense promised NATO?”

Mr. Bennett agreed that “strategic ambiguity tends to support deterrence” as long as Kim Jong-un does not want “a nuclear conflict that would almost certainly doom his regime,” but said Washington “needs to apply strategic clarity to deter North Korean provocations like ICBM test launches” and not “be intimidated by the risks of escalation.” 

Korea’s deputy national security adviser, Kim Tae-hyo, told Yonhap News that Koreans would now “feel that they are sharing nuclear weapons with the United States,” but Mr. Biden’s decision to send an American submarine possibly laden with  nuclear warheads to a Korean port was only of symbolic value. No one imagined the sub would do anything before departing for the western Pacific.

A Korean lawyer summarized the visit in tones of optimism and pessimism. “There were no mistakes,” he said.  “Everything went perfectly.”  

The lawyer, who didn’t want his name used, marveled not only at the impression that Mr. Yoon had made blending memories of the Korean War with current challenges from the North — and then remarking that the K-Pop group BTS is far better known than he is to Americans. 

On further reflection, the lawyer added that he had hoped Mr. Yoon would call boldly for American nukes to return to the South and for South Korea to develop its own nukes. In the end, he said, “We got nothing new from the summit.”