US PRESIDENT Barack Obama came into office with a vision for Global Zero — setting the world onto a path free of nuclear weapons eventually. Lofty as that goal was — or perhaps precisely because it was so lofty — it was quickly and severely tested and soon discarded in all but name. Tellingly, the US Republican party’s likely presidential candidate, Donald Trump, stirred up a nuclear hornet’s nest just as world leaders gathered for the Nuclear Security Summit, a project of President Obama launched in 2010 that seeks to secure the world’s nuclear supplies from terrorist threats and slots into the wider goal of an eventually nuclear weapons-free world. It appears that the narrow, though critical, purpose of the NSS remains an easier subject to address than whether states — and which states — should possess nuclear weapons at all. But even that narrow purpose has been undermined by multiple countries, perhaps most egregiously by Russia, which has the second largest nuclear arsenal in the world and which chose to boycott the summit.