By Paul Reynolds
World affairs correspondent, BBC News website
Hopes that relations between Nato and Russia might be heading for a period of stability have been dashed by the coincidence of an old-fashioned spying scandal and new tensions over Georgia.
Nato soldiers often carry out exercises in non-member countries
Taken separately, these events might have been merely an inconvenient detour. Taken together, they are a roadblock.
The plot had a new twist added on Tuesday when the Georgian government announced, on the eve of a Nato military exercise in Georgia, that it had foiled a Russian-inspired coup and was putting down a mutiny in one of its tank battalions.
The claim is likely to reinforce in the minds of many Nato members that, although Nato has promised eventual membership to Georgia (and Ukraine), now is not the time to commit the alliance to the defence of such an unstable country.
Georgia of course is arguing the opposite, that only Nato support can give it security.
The Nato exercise was planned a year ago, starts on 6 May and lasts a month. It will see first a command exercise (Co-operative Longbow) and then a field exercise to test for a terrorist attack on a peacekeeping operation (Co-operative Lancer 09).
About 1,000 troops will take part, from a number of Nato countries. Russia was invited but declined to be cooperative.
Another factor souring relations is a Russian decision to take over border controls in the two breakaway regions of Abkhazia and South Ossetia, whose independence Russia is supporting following its invasion in August last year.
Nato spokesman James Appathurai said that this was in "clear contravention" of agreements reached with the EU over control of the two territories.
The spying involves the expulsion from Brussels of two Russian diplomats, one of them Vasiliy Chizhov, the son of Vladimir Chizhov, the Russian ambassador to the EU, no less.
Russia's ambassador to the EU is among those embroiled in scandal
He (the son) has been linked to the case of Herman Simm, an Estonian official who has been sentenced to 12 years in prison after admitting that he handed over to the Russians thousands of pages of secret Nato documents.
Rhetoric of a kind rarely heard since the end of the Cold War has come from Moscow - that old favourite "gross provocation" has made a return and some kind of retaliation is now expected.
The Russians are muttering that some Nato members, presumably Eastern European ones, are trying to "sabotage" (another revived semantic relic) the recent improvement in ties with the US which has seen the Obama administration declaring that it wants to press the "reset button" with Moscow.
The timing of the expulsions was a bit unfortunate, as they came just as Nato and Russia had finished the first of the resumed meetings of the Nato-Russia Council.
These meetings had been suspended after the Russian military intervention in Georgia last August. This timing has of course fuelled Russian suspicions that the case is being turned to political advantage.
"This is a difficult relationship with ups and downs and it's time to hunker down," says Fraser Cameron, director of the EU-Russia centre in Brussels.
"Nato membership for both Georgia and Ukraine is on the back burner," he added.
Nato's secretary general has tried to reassure Russia
"There are very different views within Nato about how to deal with Russia. Some see Russia as an existential threat, others that it is too important for relations to be disrupted and that Russia can help in some of the big picture items like Iran and Afghanistan.
"The Russians themselves play hot and cold and also do not seem to have a clear view. They might not want to give the Americans a quick success and could let these problems fester.
"It is good that the two sides are talking, at least," Mr Cameron says.
"The US/Russian dialogue had disappeared under the Bush administration. The relationship between [Russian Foreign Minister] Lavrov and [US Secretary of State] Rice was very bad. No senior American voice was heard in Russia."
The best hope for an improvement at the moment lies in talks between the US and Russia about nuclear weapons The two sides have set themselves a deadline of December to reach an agreement.
If they do agree - and it is likely that they will because it is in both their interests to do so, given that there are plenty of nuclear weapons to cut - that will be an up. But equally there will be downs in future as well.
The basic relationship has not been worked out. There is suspicion among Nato members about the authoritarian nature of the Russian government and its determination to exercise influence over its near neighbours.
And there is suspicion in Moscow that Nato would like Russia to return to the chaotic days of the 1990s, when Russia was passive and compliant.