Joe Biden, who won the support of state and national firefighters in the spring, has long been popular in the labor movement. Elizabeth Warren is also seen as a strong labor candidate, though she has not yet secured an endorsement from a New Hampshire union.

More than a dozen New Hampshire labor leaders said Sanders no longer has a monopoly on issues important to them like he did in 2016.

This year, Gulla said, his union may not endorse a candidate before the primary, even though Sanders has now done two major events with members in the past few weeks.

Likewise, the state chapter of the International Brotherhood of Electrical Workers — which endorsed Sanders as early as fall of 2015 and then vigorously campaigned for him for more than four months — is sitting it out this year.

“Last time, it was a real strong push from the membership to go out and endorse Bernie,” said Denis R. Beaudoin, the union's business manager, adding there is no big push to endorse anyone this election: “Everybody is working, we’re all busy.”

Labor was a crucial part of Sanders’ grassroots coalition the Clinton campaign struggled to compete with, losing to him in New Hampshire by more than 22 percentage points.

“To have one of the largest unions in the state come out against their national leadership and endorse Bernie Sanders over Hillary Clinton made a huge difference in the outcome,” Kurt Ehrenberg, Sanders’ former New Hampshire political director. “It sent a signal not only to the progressive community that Bernie was for real but to the entire country that this was really going to happen, and we’re still feeling the reverberations of that today.”

Labor isn’t ditching Sanders so much as it is staying out of the primary fray. New Hampshire is following a national trend, which has seen all but a handful of unions stay out of the race. Only Biden has a large union in his camp, the International Association of Fire Fighters, but that endorsement was made by the union’s national leadership in March.

Sanders secured the endorsement of the state’s postal workers union, which represents just under a thousand people. But even that endorsement didn’t stem from a groundswell of membership support. Instead, it was a member of Sanders’ local steering committee, Janice Kelble, who recently realized the union hadn’t endorsed yet. She made a motion in front of a union meeting and it was unanimously approved by the members in attendance, about 40 people.

Sanders is leaning on long-standing relationships to shore up his support, continuing to make calls to union activists to make his case. The campaign has also tasked several staffers at the national and regional levels with boosting his labor backing, including Kevin Cooper, the deputy national political director, and Sheila Healy, the New England labor outreach director.

“We didn't do steak-and-potato dinners [in 2016], but he's doing a lot of things different this time,” said Julia Barnes, Sanders’ New Hampshire state director during the last election. “There's a much more significant political outreach program this time around.”