Canada's allies are wondering if they can still shelter under the U.S. nuclear umbrella

Gone, it seems, are the days when the phrase "going nuclear" was meant figuratively.

Since the beginning of the year and the inauguration of the second Trump administration, an increasing number of Washington's closest allies have begun to throw quiet — and sometimes not so quiet — fits about whether they can still count on the decades-old nuclear deterrent capability of the United States.

Few places feel that uncertainty more keenly than South Korea.

Faced with an erratic, often hostile, nuclear-armed neighbour in North Korea's Kim Jong-un, it probably shouldn't be surprising that recent polling has shown almost three-quarters in the democratic south are in favour of their country acquiring nuclear weapons.

While the notion of Canada acquiring nuclear weapons to guard its sovereignty is extremely remote and nowhere on the public policy radar, some of the country's key allies are actively debating what might have seemed unthinkable a few years ago.

Polish Prime Minister Donald Tusk said in early March that his country was looking at gaining access to nuclear arms — more than likely through negotiated security guarantees with France.

South Korea, which is in the midst of a presidential election campaign, doesn't have the luxury of a nearby nuclear-armed alternative to the U.S.

"As of right now, South Korea is fully reliant on an extended deterrence provided by the United States," said Ban Kil Joo, a former South Korean naval officer, at the Korea National Diplomatic Academy in Seoul.

Aside from Washington's mercurial approach to allies, the Korean republic has other reasons to be edgy.

Russia and North Korea have signed a strategic partnership that Seoul is worried includes high-tech transfers that could be used in missile technology. And North Korean troops are gaining critical battlefield experience fighting alongside Russian soldiers against Ukraine.

More significantly though, Ban said, Pyongyang quietly changed its nuclear posture recently, and that means its weapons are no longer purely defensive.

The U.S. and South Korea co-operate to contain North Korea through a bilateral agreement known as the Nuclear Consultative Group, which meets twice a year at the level of senior officials, including defence, military and intelligence.

Ban said his country would not simply and unilaterally begin pursuing nuclear weapons and he's personally doubtful it would be a wise policy, regardless.

While "all options would still need to be on the table," Ban said, "I don't think nuclear is an option [to pursue] — or be selected as an eligible or relevant policy in the government."

The enormous cost of maintaining a nuclear arsenal is one drawback, but Ban said his country doesn't want to go down that road and doesn't like the international message it sends in terms of nuclear non-proliferation.

"It is not a good sign or not a rational behavior, if South Korea is just going to make nuclear weapons without any negotiation," he said.

Having said that, South Korea has not yet signed or ratified the Treaty on the Prohibition of Nuclear Weapons, according to the International Campaign to Abolish Nuclear Weapons.

That is likely a calculated strategy on the part of the government in Seoul.

Ban said diplomacy needs to be front and centre.

"If the United States is willing to provide an upgraded nuclear deterrence to deter any type of North Korea's nuclear threat, there is no reason for South Korea to be armed with nuclear weapons," he said.

Even still, the notion of acquiring nuclear weapons does have political traction in Seoul.

Former president Yoon Suk Yeol, who was removed from office last month by the country's constitutional court after a failed attempt to declare martial law, openly endorsed the idea.

Yoo Yong-won, a member of Yoon's conservative People Power Party (PPP), launched an initiative in the National Assembly known as the Mugunghwa Forum, which aims to boost support for laying the groundwork to quickly go nuclear should the need arise.

In negotiations with Washington, much would depend on the demands the Trump administration places on South Korea.

Like Canada, the first iteration of Donald Trump's presidency saw demands that Seoul shoulder more of the burden and cost of its defence.

The government did raise defence spending, but not as much as Trump wanted, South Korea's deputy defence minister Hyunki Cho told CBC News in a recent interview.

Talks have resumed.

"I'm limited in what I can say," Cho said. "We are currently in the process of going through these negotiations, but I think I can say that I am pretty confident that President Trump will fully consider what we have done thus far as well as the position the Korean Peninsula has in the Indo-Pacific region."

At this point in the discussion, Cho said, the U.S. "has not explicitly asked" South Korea to increase defence spending. The country allocates roughly $50 billion annually — or 2.8 per cent of its gross domestic product — to defence.

Researchers at the Washington-based Center for Strategic and International Studies recently noted that the Trump administration has remained silent about whether the U.S. nuclear deterrent is in question.

Much of the uncertainty is driven by Trump's threats not to protect allies that don't meet his expectations and spending threshold.

Oddly enough, this is where Canada enters into the conversation in South Korea, which has watched the U.S. annexation bluster and economic bullying with a mixture of dismay and alarm.

The taunts to Canadian sovereignty are cause for concern, senior officials — at defence and the foreign ministries in Seoul — told CBC News during background briefings.

The sense they get is if Canada can be thrown over the side, what does that mean for them and — what do they do about it?