VERNON, N.J. — Lisa Anderson joined the New Jersey chapter of Action Together the day it formed — Nov. 7, 2016 — with a plan to celebrate Hillary Clinton’s election the next day. At 52, she had never joined a political group before. More than 2,000 others also signed up that day.

But, Ms. Anderson said, the anticipated joy quickly turned to shock and stomach-churning anxiety after President Donald J. Trump won and Action Together gatherings suddenly became “therapy sessions.”

No one talked about the coming New Jersey governor’s race. There was no mention of Gov. Chris Christie, who could not run again, or Lt. Gov. Kim Guadagno, who might run, or Philip D. Murphy, who was already running.

Yet, on a weekday afternoon 10 months later, Ms. Anderson was in heavily Republican northwest New Jersey making calls for Mr. Murphy, fighting for every vote for the Democratic candidate. It was the last thing on her mind when she decided to dive into the messy world of political activism.