On November 30, the Working Families Party set up a webpage to let anyone who visits that web page vote on whether the WFP should endorse Bernie Sanders, Hillary Clinton, or Martin O’Malley. The voting was to continue for a week.
On December 8, the party announced the results. Sanders easily won, with 87% of the total vote. The WFP will now do what it can to help Sanders become the Democratic nominee. This is the first time the WFP has made a presidential endorsement before the Democratic Party chose a nominee. See this New York Times story. Thanks to Darryl Perry for this news.
Note that there was no “run your own candidate” option on the ballot.