China has the neutron bomb.
China closely supports Iraq and AlQaeda. Bin Laden gave two US cruise missiles to China after 1998.
Red mercury used in making miniaturized neutron bombs (baseball sized)was found in Iraq by UN weapons inspectors.
It is very possible that China has helped Iraq develop a neutron bomb and that Iraq could give a suitcase neutron bomb to AlQaeda and Bin Laden to bring into the US. China for that matter could also directly give a suitcase sized neutron bomb to AlQaeda and Bin LAden.