Out on the sidewalks, 28-year-old office worker Lee Jae Sang already had an opinion about how to respond to North Korea's fast-growing capacity to lob nuclear bombs across borders and oceans.
"Our country should also develop a nuclear program. And prepare for a possible nuclear war," said Lee, voicing a desire that a February poll showed was shared by 3 out of 4 South Koreans.
It's a point that people and politicians of non-nuclear powers globally are raising more often, at what has become a destabilizing moment in more than a half-century of global nuclear nonproliferation efforts, one aggravated by the daily example of nuclear Russia tearing apart non-nuclear Ukraine.
That reconsideration by non-nuclear states is playing out in Asia. The region is home to an ever-more assertive North Korea, China, Russia and Iran, three nuclear powers and one near-nuclear power, but is unprotected by the kind of nuclear umbrella and broad defense alliance that for decades has shielded NATO countries.
Vulnerable countries will look to the lessons from Ukraine, especially whether Russia succeeds in swallowing big pieces of Ukraine while brandishing its nuclear arsenal to hold other nations at bay, as they consider keeping or pursuing nuclear weapons, security experts say.
As important, they say, is how well the U.S. and its allies are persuading other partners in Europe, the Persian Gulf and Asia to trust in the shield of U.S.-led nuclear and conventional arsenals and not pursue their own nuclear bombs.
For leaders worried about unfriendly, nuclear-armed neighbors, "they will say to their domestic audiences, `Please support our nuclear armament because look what happened to Ukraine,' right?'' said Mariana Budjeryn, a researcher with the Project on Managing the Atom at Harvard's Kennedy School of Government.
As a schoolgirl in 1980s Soviet-era Ukraine, Budjeryn drilled on how to dress radiation burns and other potential injuries of nuclear war, at a time that country housed some 5,000 of the Soviet Union's nuclear weapons. Her country renounced nuclear weapons development after the Soviet Union shattered, opting for economic assistance and integration with the West and security assurances.
"Ultimately, I think a lot is riding on the outcome of this war in terms of how we understand the value of nuclear weapons," Budjeryn said.
Around the world, the U.S. military is reassuring strategic partners who are facing nuclear-backed rivals.
Near the North Korea border this month, white-hot ballistic missiles arched through the night sky as the U.S. joined South Korea in their first joint ballistic test launches in five years. It was a pointed response to North Korea's launch of at least 18 ballistic missiles this year.
In Europe and in the Persian Gulf, President Joe Biden and U.S. generals, diplomats and troops are shuttling to countries neighboring Russia and to oil-producing countries neighboring Iran. Biden and his top lieutenants pledge the U.S. is committed to blocking nuclear threats from Iran, North Korea and others. In China, President Xi Jinping is matching an aggressive foreign policy with one of his country's biggest pushes on nuclear arms.
Some top former Asian officials have cited Ukraine in saying it's time for more non-nuclear countries to think about getting nuclear weapons, or hosting U.S. ones.
"I don't think either Japan or South Korea are eager to become nuclear weapon states. It will be immensely politically painful and internally divisive. But what are the alternatives?'' ex-Singapore Foreign Minister Bilahari Kausikan told the audience at a March defense forum.
For those hoping North Korea would give up its nuclear weapons, the example provided by Russia's invasion of Ukraine is "another nail in that coffin," Terence Roehrig, a professor of national security at the U.S. Naval War College, said at another defense forum in April.
"Ukraine is going to be another example to North Korea of states like Iraq and like Libya, that gave up their nuclear capability, and look at what happened to them,'' Roehrig said.
Ukraine never had detonation-ready nuclear bombs, at least, none it could fire on its own.
The Soviet Union's collapse left Ukraine with the world's third-largest nuclear arsenal. But Ukraine didn't have operational control. That left it with a weak hand in the 1990s when it negotiated with the U.S., Russia and others on its place in the post-Soviet world, and the fate of the Soviet arsenal. Ukraine got assurances but no guarantees regarding its security, Budjeryn said.
"A piece of paper,'' is how Ukrainian President Volodymyr Zelenskyy referred to one such assurance, signed in 1994.
The U.S. itself has given nuclear and nuclear-curious countries plenty of reasons to worry about forgoing the world's deadliest weapons.
The West compelled Libyan leader Moammar Gadhafi to give up his country's rudimentary nuclear weapons program in 2003. A couple of years later, Gadhafi's son Saif al-Islam shared with researcher Malfrid Braut-Hegghammer his father's biggest worry about that, that Western nations would support an uprising against him.
"And lo and behold, a few years later, get to 2011, you saw what happened," said Braut-Hegghammer, now a University of Oslo nuclear and security strategy professor.
What happened was NATO, at U.S. urging, intervened in a 2011 internal uprising against Gadhafi. A NATO warplane bombed his convoy. Rebels captured the Libyan leader, sexually abused him, and killed him.
In Iraq, the U.S. played a central role in forcing Saddam Hussein to give up his nuclear development program. Then the U.S. overthrew Saddam in 2003 on a spurious claim he was reassembling a nuclear weapons effort. Three years later, with Iraq still under U.S. occupation, Saddam plunged through a gallows.
The Middle East leaders' fall and brutal deaths have clouded denuclearization efforts with North Korea. Rare U.S.-North Korea talks in 2018 collapsed after the Trump administration repeatedly raised the "Libya model'' and Vice President Mike Pence threatened Kim Jong-un with Gadhafi's fate. "Ignorant and stupid,? North Korea's government responded.
Russia's invasion of Ukraine now "only highlights to some countries, at least, that if you have a nuclear weapons program, and you're sort of far along with that, giving it up is a terrible idea,'' Braut-Hegghammer said.
The world's nine nuclear powers, the United States, Russia, France, China, the United Kingdom, Pakistan, India, Israel and North Korea, hold some 13,000 nuclear weapons. Israel does not acknowledge its nuclear program.
The biggest nuclear powers historically have sought to control which countries can licitly join the club. Countries that proceed regardless, including Iran and North Korea, are isolated and sanctioned.
Nuclear experts mention South Korea and Saudi Arabia as among the countries mostly likely to consider nuclear weapons. Saudi Crown Prince Mohammed bin Salman in 2018 pledged to immediately acquire nuclear bombs if Iran did.
It's surprising that more countries haven't acquired a bomb, Jessica Cox, head of NATO's nuclear directorate, said at the April forum.
"If you look at it from a historical perspective, it is not at all clear in the 1950s and 1960s that there would be less than 10 nations armed with nuclear weapons in the world ... 70 years later.''
What made the difference in Europe was NATO's nuclear deterrence, 30 nations sharing responsibility and decision-making for a nuclear arsenal that deters attacks on them all, Cox said.
Many feel Ukraine made the right decision when it avoided possible isolation by waiving a nuclear-armed future. That gave Ukraine three decades to integrate with the world's economy and build alliances with powerful nations now aiding its defense against Russia.
As a young woman in Ukraine, Budjeryn realized at one point after the 1990s accords that her own job, then in business-development, was funded by the Clinton administration, as part of the West's rewards to Ukraine for the nuclear deal.
"If Ukraine prevails," she said, " then it will communicate that nuclear weapons are useless.''
"But if Ukraine falls, the story will look very different,'' she said.