With all of the fighting and disagreements amongst the presidential candidates, one thing they have all expressed is a fear that terrorists could acquire a nuclear weapon or the radioactive material to make a so-called “dirty bomb.” 

Beginning today, the Obama administration hosts the last of four nuclear security summits where global leaders will address the threat of nuclear terrorism. 

We talk about the summit and its goals with Will Tobey, senior fellow at Harvard’s Belfer Center for Science and International Affairs. He recently served as deputy administrator for defense nuclear nonproliferation at the National Nuclear Security Administration.