President Barack Obama's trip to Asia next week will be anchored by a stop in Hiroshima, where he will focus on its dark nuclear past.

But Obama’s visit comes at a moment when U.S. and Asian officials fear the region is entering a newly dangerous atomic future, threatening Obama’s vow to roll back the spread of nuclear arms and possibly touching off an Asian nuclear arms race.


North Korea is expanding its nuclear arsenal and upgrading its ballistic missiles. China is growing and modernizing its stockpile. Most strikingly, Pentagon planners worry that Japan and South Korea might for the first time explore developing nuclear arms of their own — promoted in part by the recent conclusion by U.S. and South Korean intelligence agencies that North Korea’s bizarre regime can now mount a small nuclear warhead on missiles capable of striking Japan and South Korea.

Then there is Donald Trump, who recently questioned one of Asia’s core security assumptions: a nuclear-weapons free Japan. “Wouldn’t you rather, in a certain sense, have Japan have nuclear weapons when North Korea has nuclear weapons?” Trump asked in a March New York Times interview. Seared by the horrors of Hiroshima and Nagasaki, Japan has forsworn nuclear weapons since World War II, though it runs a nuclear energy program.

Obama’s visit Friday to Hiroshima, which was incinerated by a U.S. atomic bomb in August 1945, will promote a message diametrically opposite from Trump’s. “It’s an opportunity to focus the world’s attention on the need to prevent the spread of nuclear weapons and seek a world without them,” said deputy national adviser Ben Rhodes.

That’s part of Obama’s broader and long-stated goal of limiting nuclear proliferation — one he has pursued with mixed results. Obama sealed a nuclear deal with Iran that stopped its path to a bomb, for now, and has led efforts to secure loose nuclear material worldwide. But he has not achieved major reductions in the U.S. nuclear arsenal, thanks in part to Russia’s resistance to making comparable cuts. Nor has he slowed dangerous atomic expansions in North Korea and Pakistan.

Now, after the Iran deal averted what Obama predicted would be a nuclear arms race in the Middle East, Asia suddenly looms large as an atomic danger zone. Seemingly immune to sanctions and isolation, North Korea presses on with its weapons program: Recent satellite imagery suggests that North Korea may be building a new tunnel in preparation for its fifth nuclear test.

Officials in Japan, South Korea and Taiwan are losing patience with international efforts to thwart Pyongyang’s program. Some suspect China is all too happy with a status quo that keeps North Korea contained and stable.

And those governments increasingly fret that the U.S., which has protected them for decades under a nuclear umbrella, may become a less reliable ally.

The issue is particularly fraught in Japan, which has a post-World War II policy of pacifism enshrined in its constitution. But last year Japan passed legislation reinterpreting its constitution to allow foreign military operations for the first time since World War II, though only ones that are defensive in nature.

Some officials and analysts say the anti-nuclear taboo is also being revisited, especially as China asserts new territorial claims, including over islands and waters claimed by Japan. At the same time, many Japanese leaders feel that Obama has not challenged Beijing forcefully enough. Trump’s suggestion that Japan and South Korea might need to fend for themselves has only exacerbated the concerns that America can no longer be relied on for protection.

“Careless American rhetoric that calls into question America’s security commitment in general and extended nuclear deterrent in particular fuels Tokyo’s security planners to develop hedging strategies,” said Patrick Cronin, senior director of the Asia-Pacific Security Program at the Center for a New American Security.

“It has often been thought that Japan has a bomb in the basement, and it would just have to assemble the parts to create a bomb,” Cronin added. “The technical challenges might actually be much greater than that, but it is the political hurdles that remain the real barriers to Japan acquiring nuclear weapons.”

Those barriers, while still high, may be eroding.

Shortly after Trump’s comments in March, for instance, the governor of Japan’s Osaka prefecture told reporters that the country should revisit the question of nuclear weapons.

“What do we do if America’s military strength [in Japan] disappears?” asked the governor, Ichiro Matsui. “Wishful thinking doesn’t get us anywhere.”

Other Japanese conservatives have made the same argument in recent years, including Shintaro Ishihara, who served as Tokyo’s governor until 2012 and said in 2011 that Japan “should absolutely possess nuclear weapons.”

Such talk has been striking to Japan experts in the U.S., who have assumed for decades that the country would remain non-nuclear. “Very few except the extreme fringes used to talk about nuclear weapons” in Japan, said Richard Samuels, director of MIT’s Center for International Studies.

Pro-nuclear weapons sentiment in Japan remains mostly on the far right, to be sure. But the same conversation is brewing in South Korea, where a 2013 poll found that two-thirds of South Koreans support developing nukes in response to its bellicose northern neighbor.

“Seoul can no longer sit idly by as the [nuclear] talks lead to no results and Washington and Beijing are busy blaming each other for their diplomatic failures,” argued an editorial in Seoul’s conservative Chosun Ilbo newspaper earlier this year.

Such talk “is driven by a deep fear of abandonment” by the U.S., Cronin said.

Obama himself was dismissive when asked at an April 1 news conference about Trump’s talk of allowing Japan and South Korea to build their own nuclear weapons, saying they reveal that “Trump doesn’t know much about foreign policy, or nuclear policy, or the Korean Peninsula, or the world generally.”

The U.S. alliance with Japan and South Korea, he added, “is one of the foundations, one of the cornerstones of our presence in the Asia-Pacific region,” he said, adding that it “has prevented the possibilities of a nuclear escalation” in the region.

“So you don’t mess with that,” Obama said.

