Getting the US and Russia to work together in Syria was always going to be difficult. Now it looks as though a diplomatic solution was from the start a mirage at best and a trick at worst.

Almost every day brings news of the further breakdown in US-Russia relations. As the death toll from Russian-Syrian aerial bombardment of Aleppo climbs,  US Secretary of State John Kerry said on Friday that Moscow should be investigated for war crimes.

This would almost certainly be a mistake. 

Certainly, the speed and apparent lack of regret with which the Kremlin has walked away from diplomacy are cause for dismay. Seemingly discredited too is the wider thesis on which the theory of Moscow's openness to a deal was built: that behind Russia's intervention on Assad's behalf was the political goal (not necessarily contingent upon the achievement of absolute military victory) of US recognition of Russia's status as a major regional power and an essential party to any resolution of the conflict, the parameters of which would have to be congruent with core Russian interests. Kerry and Lavrov have in recent times frequently met (often in Moscow) or spoken by telephone; Moscow has enjoyed the attention. 

But the breakdown of those consultations days after their most substantive outcome so far would seem to have poured cold water on the very idea that the Kremlin could or would negotiate in good faith.

As far as Syria goes, figuring out what is true is at least as hard as figuring out what to do about it. But in the popular imagination at least, Russia wants only one thing: to save a repressive regime (whatever the cost in human life) as part of Putin's wider war, driven by a despot's natural love of violence, against democracy, the West and freedom in all its forms.

To the extent that it helps justify Western sympathy for the 'rebels', this is useful propaganda. But it's scarcely conceivable that, with Assad and his government gone, Syria would today be the liberal, democratic and peaceful of Western imagination. Putin is surely right when he says that were the rebels to overthrow the government it's far more likely that Syria would resemble Iraq or Libya: awash with weapons, dominated by Islamists or rent along sectarian lines (if not all three).

Is that really in Western interests?

Nonetheless, the 'Grand Alliance' uniting the West and Russia against terrorists of all stripes that Putin called for in his address to the UN General Assembly on the 70th anniversary last year was always fanciful. The relationship was already too heavily poisoned by Ukraine. But engaging Russia diplomatically as part of the solution rather than the problem was sensible. Perhaps Moscow and Washington could impose a settlement that preserved the governing institutions of the present (secular) Syria state while liquidating Islamic State, dispensing with the Assad family and opening up opportunities for the participation of whatever remains of moderate (if not liberal) forces in Syrian society. 

That hope appears to have vanished, replaced by renewed calls from Hilary Clinton and prominent Pentagon figures for a US-imposed no-fly zone. With Russia about to deploy the S-300 anti-aircraft system, how dangerous that could prove should be obvious.

The choice facing Western governments is whether to continue supporting an armed uprising bent on uprooting a legitimate (if evidently brutal) government at the ever-increasing risk of igniting a war with that state's nuclear-armed patron, or to curb the outraged rhetoric of the past fortnight and prepare to return to the negotiating table. Transforming the West's opposition to Russian policy in Syria into a legal dispute would kill further hope for diplomacy. The law's certainties are inimical to the flexibility the latter relies on. 

In Russia the perception is widespread that Moscow is only entitled to the foreign policy that the West allows it to have. Whereas as Washington is empowered to dismiss and summon sovereigns, making and unmaking states from Iraq to Libya, Ukraine and Syria, Russia is not entitled to submit an opinion on the survival of an allied state. Certainly, it is difficult to imagine the US agreeing to desist from coming to an ally's aid on the grounds that a hostile third party was opposed to its doing so (the irrelevance of the views of third parties is the standard riposte to Russian objections to NATO expansion in Eastern Europe).

Investigations for war crimes will do nothing to persuade Moscow why it should be the case that, on Syria, it's denied the right to a foreign policy independent of the US.

Grand theories of everything should be indulged with caution. But it's difficult not to see in the Syrian imbroglio an avatar of what we might consider the great Leitmotif of our age: the reassertion, by peaceful means or violent, of the independence of politics.

On Syria the West needs to keep calling on its diplomats, not on its lawyers.