Their endorsement here.
An excerpt of their statement:
We are a grassroots organization — our members are central to our vision and our work, and that is why our members get to decide who we endorse. And it was overwhelming: We voted to endorse Don Berwick for governor.
He received over 70% of the vote, surpassing by far our 60% minimum threshhold. In a contest with four other candidates seeking endorsement, this is a remarkable achievement.