Living next to the world’s only superpower must be frustrating for the folks north of the border who don’t share our views, values and fears.

Yet the idea that Canada could demand America consult with its leaders before we shoot down a missile aimed at the United States that is over Canadian soil is the most ridiculous notion I have heard in some time.

That, however, is Canada’s position entering Tuesday’s meeting with Secretary of State Condoleezza Rice over the U.S. proposed anti-ballistic-missile system. “This is our airspace; we’re a sovereign nation, and you don’t intrude on a sovereign nation’s airspace without seeking permission,” Canadian Prime Minister Paul Martin said.

His stance evidences a childlike quality that assumes Ottawa has the ability to mandate something that it can’t possibly enforce — requiring launch approval for the United States to defend itself.

It makes it difficult to take the Canadians, who are America’s biggest trading partner and historic ally, seriously on the many other matters on which we disagree.

This is one of those times when the United States must heed its national interest. If the Canadians don’t like it, too bad. In that real world, there is nothing they can do about it.

President Bush has decided to go ahead with the missile-defense system. If the Democrats can’t stop him from doing so, only a foreign leader with a highly inflated sense of his own influence would delude himself into thinking he can.

Bush asked the Canadians to participate in the project, given our geographic proximity. Under that scenario, Canadians would be in the control center of such a system.

But Martin, apparently playing to his anti-American domestic political audience, declined the invitation, which is certainly his prerogative.

Canada and America have had a relationship similar to an old-style Catholic marriage — the partners may fight but they understand that they are destined to be joined together forever, for better or for worse.

So the Bush administration is going forward with its plans to begin construction of the anti-ballistic-missile shield. And the Canadians, who have historically lived under the U.S. defense umbrella, seem to feel they are under no real threat of attack.

In today’s terrorism-anxious world, those who suggest that an anti-missile shield might be superfluous, even if it is workable, ignore reality. The spread of nukes to rogue states such as North Korea and, perhaps Iran, argues for creating such a shield.

Meanwhile, the prudent Canadian might wonder about the reliability of, say, North Korean technology. Would you bet your country on the possibility that the crazy folks in Pyongyang might not hit Toronto when they aimed for Chicago?

I hope the Canadians are just venting. They have their reasons, after all: the bleakness of the continuing cold or their unhappiness over the cancellation of the National Hockey League season.

If they are serious, though, that is no laughing matter. It would be a shame for that Catholic couple to divorce. But there are some things in a marriage — even one of convenience — that are sacred. Being able to defend yourself is one of them.

Peter A. Brown is an editorial page columnist for the Orlando Sentinel. His column was made available through KRTcampus.