Sen. Bernie Sanders, I-Vt., says he wants to fight the “billionaire class," the signature phrase of a presidential campaign that's thrived by pitting beleaguered American workers against the rich and powerful. And as the self-described socialist continues his steady rise in the polls against Democratic primary opponent and presidential front-runner Hillary Clinton, he’s winning support from the American underdogs par excellence: trade unionists.

No major unions have made White House endorsements, and the national AFL-CIO has yet to formally back a candidate. Still, a couple of state labor federations have passed resolutions backing Sanders’ bid (even though they were rebuked in an AFL-CIO memo for breaching the federation’s endorsement process); thousands of rank-and-file union members have signed up with the grassroots Labor for Bernie network; and last week, the recently retired head of one of the nation’s largest unions joined Bernie’s campaign team as a volunteer.

In a recent interview with International Business Times -- before the AFL-CIO fired off its warning memo last week -- the head of the nation’s largest transit union cheered Sanders’ “willingness to get outside the bubble.” The Amalgamated Transit Union’s Larry Hanley did not endorse the senator, and the union, which represents some 200,000 people, hasn’t decided whom to back yet. But the ATU's Hanley credited Sanders for raising the sorts of problems, beyond bread-and-butter labor ones, that he says hurt American workers: things like unnecessary military spending, environmental degradation and prohibitively costly college tuition. Hanley becomes the first president of a major union to weigh in publicly -- and candidly -- about the Democratic primary matchup.

“This model doesn’t work,” said the outspoken labor leader in a wide-ranging conversation about national politics and the 2016 campaign. “It’s not working for our unions, it’s not working for our members, it’s not working for our people and we have to change the model. It’s not enough for us to just put our logo up on some candidate who’s gonna stand up for the status quo.”

“We are at a critical point in our history because our economy is inevitably going to be crippled by this ridiculous war spending, and our environment is teetering on the brink of disaster every day, and these are issues that have been neglected or made worse by the policies of the neocons, which obviously, includes people on both sides of the political aisle.”

In particular, Hanley praised Sanders’ support for free education at four-year public universities -- a plan that Clinton has not endorsed.

“Everybody running for president should just check that box; it shouldn’t be a hard one, but I’m waiting to see if they will,” he said. “Certainly anybody who’s running in the party that claims to represent average working people ought to be saying, ‘Yeah, you know what? There’s no reason why we have to burden our kids with debt, why we have to make them come out of college with something comparable to a mortgage to pay before they get a job.’ I mean, come on, this stuff is obvious.”

“We live in a bubble of false discussion, and both sides, Democrats and Republicans, refuse to break out of that bubble,” Hanley continued. “I think Bernie has shown more of a willingness to get outside the bubble, outside the box and have those discussions. As a consequence of that, I think he’s a very good addition to the race. I think hopefully that he will encourage people in the Democratic Party to remember where they came from and remember their roots.”

At the same time, Hanley offered some praise for Clinton. A former bus driver from the New York City borough of Staten Island, Hanley rose through the ranks of the transit union before his election to the top office in 2010. As he was serving as president of his New York City local, in 2000, he supported the then-first lady’s successful Senate campaign. “I have a long history of fond affection for Hillary Clinton -- she has stood up and done many things in her lifetime of a historic nature,” he said. Nevertheless, Hanley added -- with a flair of ambiguity -- “the truth as I know it is much more frequently expressed by Bernie, and even more than Bernie, by Elizabeth Warren.”

But unions are in a pickle: Is it worth getting behind the underdog or does it make more sense to accept conventional wisdom and plan accordingly? After all, “if the election’s between Hillary and just about any one of the Republicans that have come forward,” Hanley said, “it’s gonna look like heaven and hell.”

Another gigantic crowd! This time in Portland, Maine, where more than 7,500 came out tonight for our rally. pic.twitter.com/qEtrh54pIg — Bernie Sanders (@BernieSanders) July 7, 2015

“I’m going to confess to being conflicted, and I think as a matter of fact, the whole labor movement is conflicted over this,” Hanley said. “While we see Bernie being a champion for many of our issues, we’re anguished waiting on Hillary to take the lead on that, too.”

In the ATU at least, Hanley said, leaders are expressing more frustration with the general political climate than during the last open Democratic presidential primary. (Exasperation, in general, jibes more with Sanders’ calls for “political revolution” than Clinton’s mild-mannered liberalism.) In 2007, a few years before Hanley took over the reins, the union endorsed Hillary Clinton for president, eventually spending more than $70,000 on her failed primary campaign.

“People are united in the notion that we can’t accept the status quo, that the Democratic Party no longer is the party of Franklin Delano Roosevelt, it’s more like the party of Nelson Rockefeller and the Republicans are more like the party of the Ku Klux Klan. That’s kinda the way America’s shifted,” he said. “There is a boil going on right under the surface in America and the advantage Bernie has, by being willing to talk about this kind of stuff, is that he may just make that pot boil over.”