WASHINGTON — President Biden moved on Wednesday to bolster the American nuclear umbrella guarding South Korea and vowed that any nuclear attack by North Korea would “result in the end” of the government in Pyongyang, underscoring a broad turn from diplomacy to deterrence in response to the threat from the volatile dictatorship.
Hosting President Yoon Suk Yeol of South Korea at the White House for a state visit, Mr. Biden committed to giving Seoul a central role for the first time in strategic planning for the use of nuclear weapons in any conflict with North Korea. In return, the South disavowed any effort to pursue its own nuclear arsenal, a move Mr. Yoon briefly appeared to embrace earlier this year. Mr. Biden also announced that the United States would send American nuclear ballistic missile submarines to dock in South Korea for the first time in decades.
“Look, a nuclear attack by North Korea against the United States, its allies or partisans — partners — is unacceptable and will result in the end of whatever regime were to take such an action,” Mr. Biden said during a news conference in the Rose Garden, where he and Mr. Yoon described their agreement, called the Washington Declaration. “It’s about strengthening deterrence in response to the D.P.R.K.’s escalatory behavior and the deal is complete consultation” between the allies, Mr. Biden said, using the initials for the Democratic People’s Republic of Korea.
While past presidents had also warned North Korea that a nuclear attack on the South would result in a devastating American response, the blunt language about bringing about the end of the North Korean regime was reminiscent of Mr. Biden’s bellicose predecessor, Donald J. Trump. Mr. Trump once threatened North Korea “with fire and fury like the world has never seen” if it were to attack.
Mr. Trump later pivoted 180 degrees to open personal negotiations with Kim Jong-un, the North’s iron-fisted leader, and even declared that the two of them “fell in love,” but their talks never resulted in Mr. Kim surrendering a single weapon. And throughout the Trump presidency, and into Mr. Biden’s, the North has accelerated the expansion of its nuclear arsenal and the variety and range of its ballistic missiles.
In his public comments with Mr. Yoon on Wednesday, Mr. Biden all but abandoned any talk of a negotiated diplomatic resolution of the 30-year-old confrontation over North Korea’s nuclear ambitions. While saying he would still “seek serious and substantial diplomatic breakthroughs,” he and Mr. Yoon offered no path for doing so and instead emphasized their plans for “extended deterrence,” implicitly acknowledging that North Korea’s nuclear weapons were a reality unlikely to be reversed anytime soon.
As part of the new agreement, the United States and South Korea will create a Nuclear Consultative Group to coordinate military responses to North Korea, and Washington vowed “to make every effort to consult” with Seoul before using nuclear weapons to retaliate against the North.
Still, the agreement made clear that the American president reserves the sole authority to decide whether to launch a nuclear weapon. And Mr. Biden noted that beyond the mainly symbolic submarine visits, he had no intention of stationing nuclear weapons on the Korean Peninsula. The United States withdrew its last tactical nuclear weapons from South Korea in 1991.
Mr. Yoon’s visit came at a fraught moment between the two longtime allies after leaked disclosures made clear that the United States had intercepted private conversations within South Korea’s national security council. Classified documents made public in recent weeks recounted conversations among top South Korean officials about American pressure to provide artillery ammunition to Ukraine, despite Seoul’s policy of not arming combatants in active wars.
While South Korea has provided humanitarian aid to Ukraine, it has not supplied weapons directly to Kyiv. Seoul has said it was considering selling 155-millimeter artillery shells to Washington as long as the United States would be the “end user.” According to the leaked documents, a top South Korean official discussed the possibility of selling shells to Poland on the same condition, while understanding they would be passed along to Ukraine anyway.
The two leaders sought to ignore the disclosures on Wednesday, brushing off questions as they celebrated 70 years of alliance between the two nations. Mr. Biden treated Mr. Yoon to the full pomp and circumstance of a state visit, starting in the morning with a lavish arrival ceremony featuring a 21-gun salute, honor guard, marching band and fife and drum corps and concluding in the evening with a full-scale, black-tie state dinner, only the second of the Biden administration.
“Our alliance is an alliance of values based on our shared universal values of freedom and democracy,” Mr. Yoon said during opening statements in the Oval Office before the meeting with Mr. Biden began. “It is not a contractual alliance” but an “everlasting partnership.” In perhaps an allusion to the furor over surveillance, he added, “Together we can resolve any issues between us.”
Asked later explicitly about the leaked disclosures, Mr. Yoon offered only bland comments with no hint of outrage or consternation. “We need time to wait for the investigation results by the United States,” he said. “And we plan to continue to communicate on the matter.”
Mr. Biden made no comment on the matter at all, though he cited their “shared commitment to stand with Ukraine and defend its democracy against Russia’s assault.” He called the American-South Korean relationship the “linchpin of regional security and prosperity,” adding that “I think our partnership is ready to take on any challenges.”
The new cooperation agreement in the Washington Declaration is closely modeled on how NATO nations plan for possible nuclear conflict. While the United States has never formally adopted a “no first use” policy, officials said such a decision would almost certainly come only after the North itself used a nuclear weapon against South Korea.
“The United States commits to make every effort to consult with the R.O.K. on any possible nuclear weapons employment on the Korean Peninsula,” the declaration stated, using the initials for the Republic of Korea. At the same time, it said, “President Yoon reaffirmed the R.O.K.’s longstanding commitment to its obligations under the Nuclear Nonproliferation Treaty” not to develop nuclear weapons of its own.
The accord is notable for several reasons. First, it is intended to provide assurance to the South Korean public, where pollsters have found consistent majorities in favor of building an independent South Korean nuclear force. Mr. Yoon himself mused openly about that option early this year, though his government quickly walked the statement back.
He also raised the possibility of reintroducing American tactical nuclear weapons to South Korea, a step that his government has said in recent weeks it is no longer pursuing.
The importance of the new declaration to Mr. Yoon was clear in the Rose Garden when Mr. Biden made no explicit mention of it in his opening remarks, while the South Korean leader focused intently on it in his own. Mr. Yoon called it “an unprecedented expansion and strengthening of the extended deterrence strategy” and said that the agreed response to North Korea’s threat “has never thus far been this strong.”
“Our two countries have agreed to immediate bilateral presidential consultations in the event of North Korea’s nuclear attack and promised to respond swiftly, overwhelmingly, and decisively using the full force of the alliance, including the United States’ nuclear weapons,” Mr. Yoon said.
The second reason it is important is one the Biden administration is saying little about: It edges toward reversing the commitment, going back to the Obama administration, to reduce the role of nuclear weapons in American defense strategy. For years, the United States has been improving its non-nuclear strike options, improving the precision and power of conventional weapons that could reach any target in the world in about an hour.
John F. Kirby, a spokesman for the National Security Council, said, “I would caution anyone from thinking that there was new focus on the centrality of nuclear weapons,” despite the wording of the new declaration. “We have treaty commitments to the Republic on the peninsula,” he said, using the shorthand for the Republic of Korea, and “we want to make sure we have as many options as possible.”
But the South is looking for greater assurance of “extended deterrence,” the concept that the United States will seek to deter a North Korean nuclear strike on the South with a nuclear response — even if that risks a North Korean strike on an American city.
South Korea is a signatory to the Nuclear Nonproliferation Treaty, which prohibits it from obtaining nuclear weapons. So the commitment not to build its own weapons is not new. But nations can withdraw from the treaty, simply by providing notice to the United Nations. Only one nation has done so: North Korea, in 2003. Three countries have not signed the treaty and have developed nuclear weapons: Israel, India and Pakistan.