A bit more interesting detail as reported by The Guardian:
http://www.theguardian.com/us-news/2015/aug/10/bernie-sanders-endorsement-national-trade-union
National Nurses United, which has 185,000 members nationally and is the professions largest representative, announced its backing for Sanders at a rally with him in Oakland, California.
The decision of its executive council to announce a formal endorsement follows a poll of members said to show widespread backing for his more radical policies on healthcare and social inequality.
Although the union is well-known as one of the more leftwing labor groups, its leaders claim to be surprised at the depth of support among their largely female membership given Clintons chance of becoming Americas first female president.
When the pollsters said there was a landslide for Bernie Sanders, that didnt make a lot of sense to me initially given the fact that Hillary Clinton is a woman, director RoseAnn DeMoro told the Guardian in an interview ahead of the announcement. I thought it would be fairly balanced, and its not.
DeMoro would not disclose the internal polling numbers but said the three recent surveys represented a pretty significant sampling of the unions members and she was stunned at the level and depth of enthusiasm for Bernie.