Almost every well prepared summit produces a "surprise". This "reset" summit between the US and Russia yielded heavily trailed agreements whereby Washington will be able to use Russian airspace to carry troops and material to Afghanistan, and the two countries will cut their strategic nuclear arsenals to as few as 1,500 warheads apiece by 2016.

Less expected was President Obama's intent, declared at his joint press conference with his opposite number Dmitri Medvedev, to convene a nuclear security summit next year to tackle proliferation, with Moscow in line to host a follow-up soon afterwards.

The move not only addresses the spread of nuclear weapons, perhaps the most dangerous threat to global stability. It is also implicit US acknowledgement of Moscow's importance – a key element in any long-term improvement in ties after the recent strains between the former superpower rivals.

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Yesterday's encounter was a step forward – though it could hardly have been otherwise after the chill of the later years of the George W Bush administration. Mr Obama and Mr Medvedev, men of a similar generation, seem to have struck up a decent working relationship. Meanwhile the Foreign Minister, Sergei Lavrov, plainly gets on a good deal better with Hillary Clinton than he did with Condoleezza Rice.

But the Medvedev/Putin conundrum persists: who has the last word in Kremlin policy-making? By saying that any decision will be that of the Russian government as a whole, Mr Obama neatly sidestepped the question.

Mr Medvedev has on occasion seemed less authoritarian on domestic issues, and more conciliatory on foreign policy than his predecessor. However Vladimir Putin – now the Prime Minister – remains Russia's most popular politician, in part thanks to his uncompromising line on the US, and his insistence that the former superpower must be respected as it was before the collapse of Communism.

Polls show Mr Putin's compatriots broadly agree, for Russians remain deeply sceptical of the new US President. The most lasting success of this summit would be if Mr Obama changed Russian opinions of himself, and by extension of the country he leads.

As for the vaunted "reset", events will show whether it is more than wishful thinking in Washington. On Iran for instance, both leaders expressed concern over Tehran's nuclear ambitions. But the crunch will only come when Moscow has to decide whether to back much tougher UN sanctions against the Islamic regime, all but inevitable assuming Iran does not relent in its uranium enrichment programme.

Of Nato expansion, particularly as it relates to Georgia and Ukraine, there was little mention. Both presidents did not conceal they were divided on other major issues, most notably US plans for a missile defence system in central Europe, which could yet scupper hopes for strategic arms cuts.

On missile defence, Mr Obama flatly ruled out any direct link between the strategic arms cuts and abandonment of the missile defence system. "Under no scenario" were the installations in the Czech Republic and Poland aimed at providing protection from "the mighty Russian arsenal".

But a chink remains open: the internal US review of whether the system can actually meet its modest proclaimed goal, of dealing with what the US President called "a stray missile from a third source" (ie Iran or North Korea). If it concludes that missile defence fails that test, a deal could be possible. But Mr Obama will not give up something for nothing in this new round of nuclear bargaining.