The HRC endorsed Hillary, so it makes sense he wouldn't be happy with them.
But what exactly is the context to this?
Maddow basically asks him if he was disappointed he didn't get these endorsements since his policies line up with these organizations' goals, and if he'd competed for them, to which he replied he would have loved to have had them, and then pivoted into the establishment spiel.
Here's the link to the interview if anyone is interested:
http://www.msnbc.com/rachel-maddow/watch/sanders-up-for-more-debates-with-dnc-or-not-604730435856