President Vladimir Putin's decision to suspend Russia's participation in the Conventional Forces in Europe, or CFE, treaty is a potent political signal.
It is yet another sign of the worsening relationship between Moscow and the West.
It shows that this relationship was not improved in any substantial way by the informal meeting at the start of this month between the US and Russian presidents at the Bush family's holiday home at Kennebunkport in Maine.
It is another diplomatic warning shot from Mr Putin across the bows of the Bush administration.
And with crucial issues like Iran's nuclear programme and the political future of Kosovo looming at the United Nations, it raises a new set of questions about how far Russia might go to block initiatives backed by Washington and its key allies.
President Putin's move will be taken as yet another sign of a more assertive foreign policy - a policy buoyed up by Moscow's rising income from oil and natural gas
The Russians have been threatening to suspend their participation in the CFE treaty for several months.
An emergency meeting in mid-June to discuss the issue made little if any progress.
The CFE treaty of 1990 was one of the most significant arms control agreements of the Cold War years.
It set strict limits on the number of offensive weapons - tanks, aircraft, artillery and so on - that the members of the Warsaw Pact and Nato could deploy in a broadly-defined Europe, stretching from the Atlantic to the Urals.
In the wake of the collapse of communism, the treaty was revised in 1999, in part to address Russian concerns.
The most recent round of talks on the treaty failed
This revised treaty has never been ratified by the Nato countries who first want Russia to withdraw all of its forces from the former Soviet Republics of Georgia and Moldova. Now Russia's patience has run out.
President Putin's decree to suspend application of the treaty is not the same as a full-scale withdrawal - that would require a formal notification of the other parties.
This suspension is a unilateral Russian measure and its practical impact will be limited.
Various routine inspections, exchanges of data, and so on will presumably be halted.
In many ways the CFE treaty is not hugely relevant today.
The Cold War is over and whatever new tensions there may be between Russia and the West, nobody envisages a return to an armed stand-off on the European continent.
Nonetheless Mr Putin's decision matters.
For a start it raises questions about yet one more arms control treaty at a time when disarmament experts fear that the whole network of arms control treaties established during the Cold War years is increasingly under strain.
The United States pulled out of another key agreement, the Anti-Ballistic Missile treaty, in December 2001.
In a sense Mr Putin is just demonstrating that what the Americans can do in the name of their vital interests, so Russia can also threaten in the name of its national interest.
President Putin's move will be taken as yet another sign of a more assertive foreign policy - a policy buoyed up by Moscow's rising income from oil and natural gas.
But analysts wonder if this is really a sign of strength.
For all its energy revenues, Russia remains a shadow of the former Soviet Union in the superpower stakes.
Russian experts argue that Mr Putin realises this.
But in certain key areas, not least missile defence, he wants to be treated by Washington as an equal.
Russian opposition to US plans to deploy limited missile defence in Poland and the Czech Republic is at the heart of their current disagreements.
But Russia's ever more muscular noises that it might block a proposed United Nations deal on the political future of Kosovo adds a worrying dimension to what up to now has been largely a rhetorical row.
Add in "local difficulties" like the dispute between London and Moscow over the murder of a former Russian agent living in Britain and there is real danger that relations between Russia and the West could be heading back to the freezer.
It is clearly nonsense to speak of a new Cold War.
But several Russian foreign policy experts have expressed concern that relations could deteriorate significantly.
Mr Putin's position, they say, is more sophisticated and perhaps more nuanced than some Russian spokesmen's pronouncements might indicate.
Mr Putin has gone some way, for example, in acknowledging that Iran does represent a potential missile threat. But Mr Putin is drawing on a strong well of anti-Americanism in Russia's military and foreign policy establishment.
That is why Mr Putin's whole approach risks sounding, and indeed becoming, blunter and more dogmatic than even he probably wants.
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