President Obama’s long-awaited Nuclear Posture Review contains elements of both continuity and change in US nuclear policy.

A recrafted Negative Security Assurance, constraining US nuclear use in specific circumstances, lies at the core of the document but, overall, changes are not as grand as leading arms-controllers had hoped.

Still, for allies like Australia the broad message is that the US nuclear ‘umbrella’ is getting smaller, even if not dramatically so.