Crimea crisis quickens Nato's steps
There is an unmistakeable spring in Nato's step. Nobody here at the alliance's headquarters in Brussels is happy about the Ukrainian drama but through his seizure of Crimea, Russia's President Vladimir Putin may have given a new sense of purpose to the world's oldest and most successful military alliance.
There is, too, a real sense of crisis and a feeling that the alliance has to an extent been taken in by Moscow.
As one senior Nato official put it: "We may have had an overly optimistic view of Russia for many years."
Now the trust, he said, had gone.
In terms of the gravity of the military situation on Ukraine's frontier, Nato has been rather more forthright about what it is seeing.
Nato's top military man in Europe, General Philip Breedlove, says that some 40,000 Russian soldiers are still massed near Russia's border with Ukraine. Nato, he insists, has not seen any significant pull-back.
But it is the high level of readiness of these troops that is most alarming Nato leaders.
The general says that if ordered they could be on the move within 12 hours. He emphasises that what has been deployed "is absolutely capable of being an invading force - all of the necessary parts and pieces behind the land forces - fixed wing air (aircraft), rotary wing air (helicopters), hospitals, supplies, it's all there in case it is asked to do its job."
Gen Breedlove says that Russian forces could achieve their strategic goals within three to five days.
But what of Nato's assessment as to what Moscow's strategic goal might be?
Gen Breedlove set out for me three main possibilities.
Firstly, Russia could simply leave its forces in place as a means of coercion, seeking to intimidate Ukraine through its crucial electoral period.
Alternatively it might embark upon a limited operation inside Ukraine to secure a land-bridge to the Crimea.
Thirdly, it might mount a more extensive southern incursion with Russian forces punching across Ukraine towards Odessa and the pro-Russian Moldovan break-away enclave of Trans-Dniester.
This could be accompanied by advances elsewhere in eastern Ukraine.
Options drawn up
Gen Breedlove's military planners have been told by Nato foreign ministers to come up with a range of military options to reassure worried allies.
He told me that he is working on a series of potential deployments of land, sea and air forces to defend all of the alliance's borders with Russia.
The air element has already begun with the reinforcement of Nato-run air patrols over the Baltic republics and the US Air Force conducting exercises with its Polish counterpart.
More aircraft could soon be on their way. Nato is looking at how its standing naval forces might be used and the deployment of land forces is also being considered. The list of options should be ready by 15 April.
So much for Nato's military response.
At the diplomatic level it has suspended all practical co-operation with Russia. In practical terms this means that a joint counter-narcotics training operation for Afghanistan will end after the current session expires. Nato will look to carry on the work without the Russians.
A programme to supply spare parts and training for Russian-built helicopters supplied to the Afghan forces will also end.
Training can be provided by other countries - some of them Nato members - who operate the same aircraft - but spares may be more of a problem.
Also, a joint radar initiative that shares data between countries on Nato's borders will have the Russian part of the operation switched off.
However, the machinery of Nato-Russian co-operation will not be dismantled altogether.
Russia's mission at Nato will remain open and the bloc is willing to talk to the Russians at ambassadorial level or above, but it is clear that if there were to be future talks then Ukraine would be at the top of the agenda.
The sense of a significant shift in the security landscape of Europe comes, though, with many questions.
Is there anything that Nato can do to persuade Russia to withdraw its forces from the Ukrainian border ?
How permanent will the chill between Nato and Moscow become?
There is talk that the suspension of co-operation will continue until Russia falls back into line with international law.
Does that mean it has to give back Crimea? Is that really going to happen?
And there are questions for Nato, too.
The shock of this crisis has given the alliance a new burst of energy but will it be sufficient to convince member countries to boost defence budgets?
Might it also underscore something of a shift in the internal dynamics within Nato?
The US still wants its European partners to shoulder more of the burden and it is clear that some European countries - notably the Poles - are much more ready and willing to step into the breach.