What happens to delegates after a candidate drops out?: Yahoo News Explains

Following Super Tuesday, two front runners have emerged in the Democratic presidential primary — Former Vice President Joe Biden and Sen. Bernie Sanders. Now, Sanders and Biden must compete for the 1,991 delegates needed to secure the nomination at the Democratic National Convention in Milwaukee in July. However, more than 100 delegates have already been pledged to candidates who have dropped out of the race. So, what happens to them? Yahoo News Senior Editor Will Rahn explains.