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."