Why has it been so hard to get aid to Syrians under siege?

Aired: 1/12/2016 | 0:05:16 | Clip
The Syrian town of Madaya, which suffered for months while cut off from food and other necessities, is just the tip of the iceberg in terms of the humanitarian crisis caused by the war. William Brangham talks to the United Nations’ Kevin Kennedy, who’s monitoring the situation from Jordan.