Russia's intervention in Syria has changed the military and diplomatic dynamic in the crisis and left the US struggling to catch up.
Whatever the inconsistencies in Moscow's own policies, it has highlighted the deficiencies in Washington's approach - not least the collapse of its ailing "train and equip" programme for Syria, which was largely going nowhere.
Washington badly needs a new approach. US prestige in the region is at a low point.
Most of its allies are in one way or another negotiating with Moscow, and the clear message is that any new diplomatic path will run through the Russian capital rather than Washington.
Moscow's air strikes have overwhelmingly targeted non-Islamic State (IS) groups and to that extent have actually assisted the so-called IS.
Indicative of the ailing US policy is that the frequency of US air strikes against IS targets in Syria has slowed significantly since the Russian air campaign began in early September.
So US Defence Secretary Ashton Carter's appearance before the influential Senate Armed Services Committee provided an opportunity for the Obama administration to set out a new policy, to reflect the changing dynamics in the region.
What he delivered, though, was far from new - and his comments raise all sorts of questions about the scale and scope of any future US military involvement.
US deeply conflicted
Two things should be clear from the outset.
Image copyrightGetty ImagesThe US can no more than Russia resolve the twin crises in Syria and Iraq from the outside.
That depends upon key regional actors and probably most of all upon the various factions engaged on the ground.
Secondly, the Obama administration is deeply conflicted on intervention in the Middle East.
After all - in the wake of Afghanistan and Iraq - US President Barack Obama cast his foreign policy as one that would withdraw US troops from foreign wars, not engage in new ones.
That policy has had to be modified in the light of the circumstances in Afghanistan.
And we are now seeing the start of the equivalent adjustment for Iraq and Syria.
Before the committee, the US Defence Secretary spoke of a policy guided by what he called the "three Rs", namely "Raqqa, Ramadi and raids".
- Raqqa, in Syria, is the IS capital and centre of gravity. The new US equipping programme is set to help opposition forces advancing on the city, some of which, Mr Carter said, were only 30 miles (50km) from their objective
- Ramadi, the capital of Iraq's Anbar province, represents a test case for the US effort to encourage the Shia-dominated Iraqi government to reach out to local Sunni forces to defeat IS
- "Raids" was a reference to a mission last week by Iraqi Kurdish forces backed up by US Special Operations Forces - a signal the US is going to step up direct action against IS, either with its allies or in some cases with its own forces
Much of this remains highly tentative and subject to the same limitations US policy has suffered from the outset - apart from the Kurds, the US lacks effective allies on the ground.
Image copyrightPAFurthermore, many of the anti-IS forces also opposed to Syrian President Bashar al-Assad are either linked to al-Qaeda or more heavily influenced by Turkey or the Gulf States rather than by Washington.
Then there is the question of how much additional military force the US itself is willing to bring to bear.
There is talk of deploying a small number of Apache attack helicopters to Iraq.
That could involve hundreds of extra US personnel.
The question of deploying forward air controllers to maximise the air campaign's impact is also being raised again.
And the new "raiding" policy similarly has many uncertainties.
The mission last week that freed dozens of IS-held prisoners cost the life of one US serviceman, and the Pentagon has been far from clear as to the precise role of US forces in that mission.
A more active policy could well lead to further US casualties, with perhaps only limited tactical results.
Image copyrightAPWhy is there a war in Syria?
Anti-government protests developed into a civil war that, four years on, has ground to a stalemate, with the Assad government, Islamic State, an array of Syrian rebels and Kurdish fighters all holding territory.
Who is fighting whom?
Government forces concentrated in Damascus and the centre and west of Syria are fighting the jihadists of Islamic State and al-Nusra Front, as well as less numerous so-called "moderate" rebel groups, who are strongest in the north and east. These groups are also battling each other.
What is the human cost?
More than 250,000 Syrians have been killed and a million injured. Some 11 million others have been forced from their homes, of whom four million have fled abroad - including growing numbers who are making the dangerous journey to Europe.
How has the world reacted?
Iran, Russia and Lebanon's Hezbollah movement are propping up the Alawite-led Assad government, while Turkey, Saudi Arabia and Qatar back the more moderate Sunni-dominated opposition, along with the US, UK and France. Hezbollah and Iran are believed to have troops and officers on the ground, while a Western-led coalition and Russia are carrying out air strikes.
