National Nurses United, an activist union with a history of bold political moves and issue-focused campaigning, has endorsed Bernie Sanders for the Democratic presidential nomination. This is the first endorsement from a major union for Sanders, who has worked closely with NNU on a number of issues over the years.

“Bernie’s issues align with nurses from top to bottom,” said NNU executive director RoseAnn DeMoro, who ticked off issues of agreement: “insisting that healthcare for everyone is a right not a privilege, protecting Social Security and Medicare from those who want to destroy or privatize it and working to expand both, holding Wall Street accountable for the damage it has done to our communities, understanding the threat to public health from the climate crisis, environmental degradation, and the Trans-Pacific Partnership, support for minimum nurse-to-patient ratios for hospital patients, and on and on.”

Sanders echoed the sentiment, explaining that, “Like NNU, I have argued for a very long time that we have to move toward a Medicare for all, single-payer system. The United States is the only major country on earth that doesn’t guarantee health care to all people as a right and that’s an issue that must be addressed if we are going to begin to address a whole range of other challenges.”

NNU, which represents 185,000 nurses nationwide, is the first national union to endorse Sanders’ insurgent challenge to Democratic frontrunner Hillary Clinton. The AFL-CIO has not endorsed in the Democratic race and most unions have followed the lead of the federation. But the 1.6-million American Federation of Teachers, which has a strong presence in the New York and which worked closely with Clinton when she was a senator representing that state, endorsed the frontrunner in July, with union president Randi Weingarten declaring that, “Hillary Clinton, a product of public schools herself, believes in the promise of public education.”

Clinton, Sanders, and former Maryland Governor Martin O’Malley have been meeting with unions, and generally getting high marks. Former Virginia Senator Jim Webb and former Rhode Island Governor Lincoln Chafee have also met with key union leaders, and appeared as some forums. Among the Republican contenders, only former Arkansas Governor Mike Huckabee, who had support from the International Union of Painters and Allied Trades and the International Association of Machinists and Aerospace Workers when he sought the presidency in 2008, met this year with the AFL-CIO’s executive council.

The AFL-CIO has not made early endorsements in recent contested races for the Democratic presidential nod, although individual unions that are affiliated with the federation often back candidates during the caucus and primary process. For instance, in 2008, Clinton was backed by the powerful American Federation of State County and Municipal Employees, the Machinists, and the AFT, while Barack Obama enjoyed the support of the Change to Win coalition and unions such as the Service Employees, the Teamsters, and the United Food and Commercial Workers. Early on, the United Steelworkers and the Transport Workers Union backed former North Carolina Senator John Edwards, but after Edwards quit the race those unions switched to Obama.

Since its founding in 2009 (with the affiliation of the California Nurses Association/National Nurses Organizing Committee, the former United American Nurses, and the Massachusetts Nurses Association), NNU has been especially active in state races, playing a critical role in backing Jerry Brown’s 2010 run for governor of California, and has supported congressional allies such as Congresswoman Barbara Lee, D-California and Congressmen John Conyers, D-Michigan, and Congressman Keith Ellison, D-Minnesota. The union also backed Obama’s reelection campaign. But its primary focus nationally has been on a series of campaigns: the “Medicare for All” push, a “Main Street Contract” initiative that highlights many of the demands of labor rights and Occupy activists, a “Nurses Campaign to Heal America” that has focused attention on poverty, hunger, environmental racism, and climate change, and a “Robin Hood Tax USA” that proposes to implement a small tax on Wall Street transactions and steer hundreds of billions of dollars annually in revenue to health care and education.

Sanders is the Senate sponsor of the transactions tax proposal and has often appeared at NNU forums, rallies, marches, and protests over the years. That was a factor in the decision to endorse the senator, said DeMoro, who announced the endorsement by declaring, “Most Presidential candidates take money from billionaires. Bernie wants to take money from the billionaires too – by taxing them to fund a civil society with the health care, the jobs, the housing, the education, and the environmental protections that people need.”

Another factor was an internal poll that revealed what DeMoro referred to as “a level of support for Bernie Sanders that was so overwhelming that, honestly, it stunned us.”

“Nurses know Bernie has been there for them on the issues that matter to them,” explained DeMoro. “That’s something that I think most of the media misses. Bernie has been there for a lot of union members, for a lot of workers, for a long time. That’s going to be a factor in how unions access his candidacy.”

Her point is well taken, but that does not mean that Sanders will necessarily get the endorsement of every union he has worked with. Some will join the AFT in backing Clinton, who also has maintained long-term relationships with a number of major unions. Others will avoid making endorsements, as least until after Democratic debates begin in October. And if Vice President Joe Biden gets into the contest, then a lot of bets are off because Biden has maintained close ties to major unions across more than 40 years in politics.

For Sanders, however, the NNU endorsement is a valued one. When he met with the AFL-CIO in late July, the senator reportedly told the union crowd, “I see myself as part of you. This is not a conventional moment, we are fighting for the future of this country.’”