There can be no retreat. Having already had a long and distinguished past as a critic of NATO, US foreign policy and the intricately structured madness of nuclear weapons, there would be nothing more incongruent for Jeremy Corbyn, if, having become leader of a revitalised Labour Party, he were to suddenly shift, to, as Owen Jones has suggested, 'playing a constructive role within the Alliance.' Any attempt at such triangulation may represent political suicide.
This doesn't necessarily mean that Corbyn will be able to entirely prevent early steps to replace Trident, or engineer a quick exit from NATO. Whilst preventing arms sales to certain states can be done quickly by a government in office, any attempt to diversify the defence industry would take some years to implement, and still longer to fully bear fruit.
In terms of alliances and partnerships, lessons learnt between 1997 and 2010 will dominate. Leaving aside the difficulties and ethical complexities of the military campaign in Kosovo, Robin Cook was to quickly learn when trying to implement an 'ethical foreign policy' that the dynamics of the trans-Atlantic 'special relationship' have a deadening grip upon the UK's scope to determine an independent and cohesive foreign policy. As James Meek has pointed out, the more the UK shadowed the US through different expeditions in Afghanistan, Iraq and then Afghanistan again, the more the UK was exposed as lacking human, material and intellectual resources. The moral failure, and eventual military failure, of the 2003 Iraq War may well eventually be seen as a watershed moment in British foreign policy - equivalent to Suez in 1956. The initial demand for a socialist foreign policy is to work out a new operating model in response to the UK's changed - and in many ways reduced - circumstances.
