Good post from the Arms Control Wonk Jeffrey Lewis on 'extended deterrence', the US threat to retaliate with nuclear weapons on behalf of an ally. Such a posture requires the ability not only to deter adversaries but to reassure allies that the US is sincere in its pledge to use nuclear weapons on their behalf if they must.
The Lowy Institute recently hosted a panel discussion on nuclear disarmament, which you can watch on our website but is also available via ForaTV. Fora has also posted a short clip from the event on YouTube, which happens to be the moment that my colleague Rory Medcalf discusses extended deterrence, and the problems that a smaller US arsenal might cause for allies like Japan, who may feel less reassured as a result.
As Rory says, one of the big hurdles to nuclear disarmament (which both he and I favour) is the reassurance that US allies such as Japan get from extended deterrence. Same goes for Australia. The last Defence White Paper demonstrated that extended deterrence remains at the heart of our security posture, yet Australia is committed to the abolition of nuclear weapons. At some point we're going to have to square that circle.