America's formal notice of its decision to withdraw from the anti-ballistic missile treaty came as an untheatrical written notification, hardly noticed amid the rush of events. Nonetheless, it is a big moment: the announcement marks the end of a 38-year era, dating back to the 1963 test-ban treaty, through various incarnations of ABM, Salt and Start. Now it's finish.
"I have concluded the ABM treaty hinders our government's ability to develop ways to protect our people from future terrorist or rogue state missile attacks," President George Bush said.
Throughout the closing three decades of the cold war, American and Russian leaders would warily face up to each other - sometimes finding it hard to conceal their mutual incomprehension - but the process produced treaty after treaty that reduced, with surprising steadiness, the world's fear of mass destruction.
Now there is a total reversal. On the one hand, George Bush and the Russian president, Vladimir Putin, are best buddies, having established what anthropologists call a joking relationship over a Texas barbecue. On the other, the US is abrogating an international treaty, which is unprecedented in modern history.
In normal times, such a move would have thunderous domestic political consequences. Under present circumstances, it is hard to imagine what Mr Bush could not safely announce, as long as it could somehow be spun as a measure in defense of the American people.
There are opposing voices, including important ones in the Senate, but they are neither loud nor resonant.
The diplomatic effects will be muted too. But on that front the consequences are easier to envisage. Very slowly, but nonetheless surely, the US is spending the international reserve of sympathy and goodwill it accumulated on September 11, and it is now possible to imagine a moment - a long way off yet - when bankruptcy might ensue.
Russian sources here are quite frank that this is part of the thinking behind their calculated calmness. If the worst came to the worst, and they had to start increasing their nuclear weapons, they believe they could do so by adding extra warheads to existing missiles. But they don't anticipate that, so they are perfectly happy to have the moral high ground.
This announcement, and the Russians' stoic reaction, gives the Putin government further leverage in western Europe that may come in very handy in the coming months and years. The Bush government's intentions and instincts are a shared concern, right across Europe and Asia, not necessarily excluding the UK.
Outside the state department, this is a matter of little immediate concern here.
"The Europeans have always been very conservative in their approach to anything that might upset equilibrium," retired general Bernard Trainor, a pro-Bush military analyst, sniffed yesterday.
Perhaps Europe will get the message from this: the administration did not change fundamentally on September 11. Karl Rove, the president's political strategist, said it out loud this week: "He is the same president now as he was before. What you see is what you get."
What we saw, from the moment the Bush team moved into the White House in January, was that international opinion and, indeed, commitments were secondary considerations. This decision comes from the same mindset that has kept the US away from everyone else's line of thought on global warming. You might call it unilateralism, though the Bushites would prefer to call it self-reliance. And it did not waver in the weeks of coalition-building that followed the attacks.
The traditional free world had to join the coalition, because the casus belli was beyond dispute. Countries that might have wavered - Russia, China, Pakistan - were kept firmly on side because the US was able to offer massive inducements on the one hand and some alarming threats on the other. There was never a hint of apology for what many saw as the White House's earlier instinctive contempt for the outside world.
It was reasonable to imagine, immediately after the attacks, that missile defense might vanish from the agenda. If the only global superpower could be terrorized by a handful of desperate men with box-cutters, and by what might be a solitary mad scientist armed with a job-lot of anthrax germs, what use could missile defense possibly be?
That remains a reasonable line of thought, shared by many people round the world. It just happens not to be shared by the president of the United States.
© Guardian Newspapers Limited 2001