(Tribune News Service) — South Korean President Yoon Suk Yeol has received the red-carpet treatment this week as Washington and Seoul mark the 70th anniversary of their alliance. Yoon's weeklong itinerary features a high-profile summit with President Joe Biden, a glittering state banquet — an honor reserved for America's closest allies — and a joint address to Congress.

But beneath the pomp and ceremony, thorny issues are at stake. South Korean companies are worried about how Biden's efforts to promote American manufacturing and limit the growth of China's high-tech sector might affect them. And earlier this year, a leak of classified Pentagon documents revealed details of U.S. espionage against South Korea, embarrassing both countries and causing political headaches for Yoon.

Both countries are also hoping to counter North Korea's aggressive missile testing. The two leaders unveiled a new agreement Wednesday to bolster extended deterrence — the idea that the U.S. will defend its allies with its full military capabilities, including nuclear weapons — in response to mounting threats from North Korea.

Called the Washington Declaration, the agreement will give South Korea more insight and input into U.S. military planning and strengthen training between the two nations in exchange for Seoul's commitment to not develop its own nuclear weapons. The U.S. will also send a ballistic missile submarine on routine visits to South Korea for the first time since the 1980s as a visible demonstration of U.S. military might.

Biden called the nations' alliance "ironclad" and delivered a stark warning to Pyongyang during a joint news conference Tuesday afternoon in the White House Rose Garden.

"A nuclear attack by North Korea against the United States or its allies and partners is unacceptable and will result in the end of whatever regime were to take such an action," he said, adding that the U.S. remained open to diplomatic talks to "bolster stability on the peninsula."

Yoon vowed to respond to any nuclear attack "swiftly, overwhelmingly and decisively using the full force of the alliance, including U.S. nuclear weapons."

The two leaders rolled out a suite of other initiatives to cooperate on cybersecurity, economic investments and other areas to further solidify the alliance in the face of North Korea's record number of nuclear missile tests this year.

Yoon's visit is a "springboard for connecting Korea to this broader web of alliance relationships in the region, whether we're talking about security cooperation (or) economic security issues ... and interacting with other stakeholders in the region, including Southeast Asian countries and Pacific Islands," said Nicholas Szechenyi, deputy director for Asia at the Center for Strategic and International Studies, a Washington-based think tank.

Yoon, a conservative politician who came to office last year, has made fortifying military and diplomatic ties with the U.S. a centerpiece of his foreign policy. He resumed joint military exercises with the United States, coordinated with the U.S. to decrease reliance on China for global supply chains and, more critically, thawed relations with Japan despite a bitter historical dispute over Korean forced labor during Tokyo's colonial rule — a decision that prompted domestic backlash.

At Tuesday's news conference, Biden thanked Yoon for his "political courage and personal commitment to diplomacy with Japan."

Even as North Korea is a priority for the U.S. and South Korea, it's a perennial issue that both countries are aligned on, according to Victor Cha, Korea chair at the Center for Strategic and International Studies.

Still, "the subtext is China," Cha said.

As Washington intensifies its economic confrontation with Beijing, Biden is working to shore up U.S. influence throughout the Indo-Pacific region. He will host Philippine President Ferdinand Marcos Jr. at the White House next week, and is set to travel to Japan for the Group of 7 summit in Hiroshima on May 19-21.

Biden has tried to quiet South Korean companies' concerns about their ineligibility for subsidies under his Inflation Reduction Act, which provides tax credits for electric vehicles that are assembled in North America or include key components that are sourced domestically. South Korean companies do not currently qualify. Before Yoon arrived at the White House, General Motors and South Korea's Hyundai announced billions in new investment to produce electric vehicle battery cells in the U.S. with South Korean battery makers.

But Biden will have to resolve frictions over the $50 billion CHIPS and Science Act. The law gives federal funds to semiconductor manufacturers that agree to limit advanced chip production in China over the next 10 years. U.S. export controls on computer chip equipment designed to choke China's access to the advanced technology have also rankled Seoul. Japan and the Netherlands have imposed similar restrictions.

South Korean companies Samsung and SK Hynix received a one-year exemption from the U.S. export ban, but a solution will have to be negotiated when it expires in October.

"South Korea is very much reliant on its semiconductor industry as part of its broader economic strength, and that industry is heavily invested in China," said Frank Aum, an expert on Northeastern Asia at the U.S. Institute of Peace.

Yoon is under pressure to return from his visit to the White House with further assurance of Washington's dedication to trade arrangements and defense against the nuclear-armed Pyongyang as he looks to smooth over relations following the leak of classified documents.

The leaked intelligence showed that top South Korean officials were concerned that ammunition South Korea sold to the U.S. would wind up in Ukraine, violating the country's policy of not supplying lethal aid to countries in conflict. The revelation prompted criticism back home, but White House officials have brushed off any tensions caused by the breach.

Yoon told reporters the two nations were "communicating and sharing necessary information" but declined to say whether Biden had provided him any assurances.

Scott Snyder, senior fellow for Korea studies at the Council on Foreign Relations, said today's relationship with Seoul has to be "an alliance powered by chips, batteries and clean technology," but that there are "drag" issues that complicate ties, including the recently leaked Pentagon documents and the South Korean public's reluctance to get involved in Ukraine.

"It's a little bit ironic, because I think that the alliance is probably at its highest point that it's been, maybe in the (70-year) history of the alliance, in terms of intensity and depth of coordination and ... breadth of scope," Snyder said. "And yet, at the same time, there are these underlying issues of trust that are there that could trip things up and might have a negative impact on President Yoon's public approval."

Yoon began his six-day visit Tuesday by touring a NASA facility with Vice President Kamala Harris, and later laid a wreath at the Korean War Veterans Memorial with his wife, Kim Keon Hee, Biden and first lady Jill Biden.

He also met with Netflix co-Chief Executive Ted Sarandos, who announced the streaming giant would invest $2.5 billion in Korean entertainment over the next four years. Yoon is expected to meet with studio executives from Disney, Sony Pictures and others at the Motion Picture Association headquarters in Washington on Thursday.

“It’s a new frontier for the alliance,” Cha said, “beyond the sort of traditional security and free trade components of the relationship.”

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