Calls for military intervention to relieve the suffering of civilians trapped in eastern Aleppo reached fever pitch this week. Syrian and Russian aircraft bombed the rebel-held sections of the city while Syrian artillery added to the destruction.
The UN's High Commissioner for Human Rights said that the use of weapons with indiscriminate effects, by both sides, may amount to war crimes. The United States broke off bilateral contacts with Moscow on the Syrian issue in protest at the continuing assault on Aleppo. John McCain criticised Obama's Syria policy and called for the grounding of Syrian aircraft, the creation of greater risk for Russian aircraft, setting up and protecting safe zones for civilians and more robust arming of vetted Syrian opposition groups.
It is likely that Assad's forces will prevail in Aleppo and it is equally likely that Washington will do nothing to stop it because there is little if anything that it could do. Syria has never been in Washington's orbit and therefore it has had little strategic leverage and the shallowest of roots. In contrast, Damascus signed a Treaty of Friendship and Cooperation with Moscow in 1980, has hosted the Russian naval facility in Tartus since 1971 and has been using Soviet and Russian military equipment since the 1950s. Economic investment and people to people links between Russia and Syria are significant. In addition, Iran has lost several hundred of its own troops and allied Shi'a militia in propping up the regime and has given lines of credit worth around five billion dollars since the war began. Tehran has a less historical relationship with Syria than does Russia, but it sees the country as arguably more central to its strategic aims.
What this means is that Russia and Iran are invested strategically, economically and historically in Syria and their strategic aims are broadly in sympathy and quite straightforward - bolster the Assad regime against any group that opposes it so that Syria remains their strategic partner. They have accepted the costs of doing so already and there is little indication that they would be unwilling or incapable of accepting significantly increased costs.
The dilemma for Washington is that they have never been as strategically engaged in Syria as their competitors, have a range of regional partners some of whom have been pursuing their own narrow self-interests, while at the same time President Obama is trying to achieve replacing Bashar al-Assad while targeting some armed opposition groups, supporting others and remaining neutral towards a third group. All the while avoiding decisive engagement in Syria and running a military campaign in Iraq.
Obama has been criticised for his minimalist approach in Syria but none of his critics have come up with coherent or workable alternatives or plans that could end the Syrian civil war without needing to deploy large numbers of ground troops. No-fly zone advocates ignore ground-based artillery and rocket systems that are equally destructive, much more numerous and not affected by weather. Nor do they say how they will prevent jihadist groups from using coalition air cover to plan, train and re-equip within no-fly or safe zones. Or what they will do when Russia and Iran up the ante by deploying more indirect fire assets or more Russian air power or use Russian cruise missiles to hit targets.
The reality is that Russia and Iran have a much simpler aim to achieve and a more unified coalition with which to achieve it, consider Syria as historically and strategically more important to them than the US and therefore possess a greater risk tolerance in achieving those aims. Tehran and Moscow also have a much greater public threshold for casualties in Syria. Syria matters to them in a way that it never has for Washington and the retaking of Aleppo with both Iranian and Russian support is designed to send a message to the present and future US administrations - the Syrian coalition will do what it takes to protect their strategic interests and reassert control. Whether they can ever generate enough combat power to actually do that is questionable. But the question that proponents of a more robust US military intervention need to answer is how much force must be used, and in what way, to modify the behaviour not just of Damascus, but of Tehran and Moscow as well.
Dr Rodger Shanahan is a research fellow at the Lowy Institute for International Policy.
Photo by Flickr user Stefan de Vries.