What is Putin's end game in Syria?
With Western policy on Syria in a state of flux could the timing of Russia's military move into that country be more perfect?
The operation to move dozens of combat aircraft and hundreds of troops to the aid of President Bashar al-Assad must have been given the green light some weeks ago, but think of what's been happening during the past 10 days as reports emerged of the Russians appearing at an air base near the Assad stronghold of Latakia.
With American policy stalled and arguments about the degree to which its bombing campaign has blunted Islamic State (IS), the president's envoy, retired General John Allen, and several other senior officials have decided to step down. Gen Allen was known to believe the US should harden its position on the overthrow of President Assad, and in the need for a safe zone in the north of Syria - instead the prospect seems to be slipping away of either happening.
Last week the US general running Central Command, the Pentagon's Middle East arm, went through humiliating testimony in front of the Senate Armed Services Committee in which he had to admit that the number of Syrian rebels trained under a $500m (£325m) US programme who had actually made it into the field could be counted on the fingers of one hand, and that plans for a safe area in northern Syria to protect civilians would be meaningless without ground troops, but he could not recommend the commitment of US soldiers on such a mission.
As for Britain, last week the National Security Council was considering ambitious proposals to commit forces to help protect civilians in northern Syria.
This week they are facing up to the possibility that the aircraft pounding rebel held areas might soon be Russian instead of Syrian.
Other countries - from France to the Netherlands, and Australia - are either thinking of starting strikes against targets in Syria belonging to the so-called Islamic State or have recently begun them.
Will many Syrians now assume that such missions are all part of the same effort to save President Assad's government that Russia seems set to launch?
All calculations in the region have been thrown into disarray by the speed and scale of Russia's deployment.
And on social media on Tuesday morning I noted two eminent professors of strategic studies discussing "Putin envy" among their Western colleagues.
It's been evident since late August that Israel expected the imminent deployment of Russian fighter squadrons - the Americans chose to stall for a few days before giving any response to these early stories, mindful presumably that President Putin was about to commit on the ground in a way President Obama has dreaded doing since the outbreak of the Syrian civil war four years ago.
From 20 August shipments of equipment from Black Sea ports, via the Bosphorus, to the Syrian port of Tartous started picking up.
The operation followed a logical military pattern: secure the Latakia airfield; improve its facilities; create a defence against possible air attack; and lastly, bring in your combat aircraft.
Then dozens of flights by heavy Antonov cargo planes started augmenting the sea lift.
As of Tuesday morning the Russians had moved in 28 combat jets (12 Su24 bombers, 12 Su25 ground attack aircraft and 4 Su-30 multi-role fighters), two types of drones, and 20 helicopters (a mix of gunships and troop carriers).
Some reports suggest that the deployment is getting so large that it will need more than one airfield for its operations, and indeed the latest satellite pictures of the Syrian coastal region suggest that other military facilities may be under preparation for further deployments.
Pentagon officials were briefing on Monday, that the drones were already operating, presumably searching for targets, and that offensive air operations could be expected "within days".
The Russians, in a fortnight, have moved in a striking force of roughly equivalent power to the few dozen surviving capable aircraft at Syria's disposal - but with more modern guided weapons and surveillance systems.
This initiative, just like the Kremlin's moves in Ukraine last year, strikes at a delicate transatlantic seam.
There are clear differences of perspective between the White House, and some European allies that are receiving hundreds of thousands of refugees from Syria.
The Daily Beast, canvassing US officials on Monday, reported: "Privately, many seemed to welcome a Russian intervention if it alleviated the burden on the US for fighting ISIS."
In the UK however, with a government canvassing for a parliamentary vote on military action, and on the verge of pledging support to a no-fly zone to stop Syrian bombing in the north of the country, Russia's action is profoundly troubling.
Assad's bombardments have been the cause of most casualties in the war, and indeed of millions fleeing their homes.
But with the prospect of Russian muscle being added to that effort, Britain can see even more refugees being created, and enforcing a no-fly zone against Mr Putin's air force risks hideous escalation.
It is the need to prevent people shooting down one another's planes by accident that has caused the Americans and Israelis to make liaison or "deconfliction" arrangements swiftly with Russia.
The arrival in Moscow on Monday of Israeli Prime Minister Benjamin Netanyahu with his army chief of staff and head of military intelligence for unprecedented discussions with the Russian military is a measure of how far the Kremlin's move deserves that often overused term "game changer".
If there is widespread admiration among strategists and military people in Western countries of Mr Putin's tactical sense, willingness to embrace risk, and desire to show up the emptiness of western political rhetoric, there is also a body of thought that he has no bigger plan, and indeed that his actions in the past 18 months have cost thousands of lives in Ukraine as well as bringing enormous economic costs to Russia.
What is his end game? Will Syria be his Afghanistan?
Mr Putin has given public explanations of what he is trying to achieve.
Sitting next to Mr Netanyahu yesterday he said, "our main goal is to protect the Syrian state".
Scoffing at Israeli fears that Syria intended to sponsor militant attacks across the Golan Heights, Mr Putin told his visitor that the Syrian army was in no state to open a second front.
The Kremlin's objective, stated plainly, has been to prevent an implosion of the Syrian state - or what's left of it. Mr Putin last week said he intended to prevent a complete implosion of government authority of the kind that happened in Libya, following Nato's 2011 intervention there.
It's a smart message, that taps into Western guilt about what has happened since Colonel Gaddafi's overthrow.
What's more, the idea of preserving the Syrian armed forces and security agencies, while working towards a transitional government or peace process finds some support in Western countries, and indeed the American line has shifted significantly in recent days to allow President Assad to remain in power for the time being, making his removal subsidiary to the aim of crushing Islamic State.
Syrian opposition groups are already disregarding the subtleties of this message - fearing that Washington's shift and its military coordination with Russia are signs it is effectively now siding with Assad.
What nobody knows is whether Russia will continue sending ground forces to Syria - and deploy them with aims more offensive than protecting its air and naval facilities.
There have already been reports of Russians fighting on front lines, but so far in numbers sufficiently small to make little difference.
Perhaps Mr Putin's speech at the UN in New York next week will give us an idea of his broader plan - and indeed how far the US and others might have acquiesced to it.
But for now, we can watch events on the ground, asking in the coming weeks: when will strikes start? What will their targeting tell us? How will Russia react if its personnel are captured? And will larger ground forces be deployed?