Why is this single 36-inch pipe causing so much debate? CNN's Tom Foreman explains. <script type='text/javascript' src='http://i.cdn.turner.com/cnn/van/resources/scripts/van-widgets.js'></script> <div data-cnnvansinglewidget data-affiliate='gantdaily' data-videoid='bestoftv/2014/11/18/orig-the-keystone-pipeline-explained.cnn' data-size='auto' data-autostart='true'></div>