OAKLAND — Sen. Bernie Sanders was assumed to be the easy-to-ignore also-ran in the Democratic presidential primary, but, as the trending hashtag proclaims, America has begun to “feel the Bern.”

The self-dubbed democratic socialist is packing tens of thousands of revved-up supporters into sports arenas; amassing more individual campaign contributors than any other presidential candidate; and, most notably, trailing Hillary Clinton by only 6.6 points in recent New Hampshire polls.

Sanders’ burgeoning campaign rode that momentum into the Bay Area on Monday so he could collect his first national labor union endorsement and deliver one of his trademark tirades against income inequality and for universal health care.

“What our campaign is about is creating a political revolution which says to the billionaire class, they can’t have it all — this country and our government belong to all of us,” Sanders said Monday, his shirt sleeves pushed up and his finger jabbing as a redshirted throng of union members cheered at the National Nurses United and California Nurses Association headquarters.

Sanders, 73, remains far behind Clinton outside New Hampshire, but the independent senator from Vermont undeniably is giving Democrats — many of whom believed the primary race to be no race at all — something to talk about. While reality television star Donald Trump has run roughshod over the Republican field with ego-driven bluster, Sanders’ progressive populism has blossomed into a full-throated liberal uprising.

Joined Monday by video conference with thousands of nurses in cities across the nation, Sanders said he would pursue a Medicare-for-all, single-payer universal health care system; more funding for veterans’ health care; national safety standards on nurse-to-patient ratios; and new controls on prescription drug prices.

“We have to change the health care system in America and we have to change boldly and fundamentally the priorities of this nation,” he told an adoring crowd, “so that every American can experience the right to live with dignity and so that not all of our wealth is going to the top 1 percent.”

He also called for a faster transition to sustainable energy in order to combat climate change; a “Robin Hood” tax on Wall Street speculation to fund college education for all; public financing of election campaigns; and stronger protections for labor organizing.

Despite recent momentum, Sanders remains a long shot. He still trails Clinton by 36 percentage points in an average of five recent national polls compiled by Real Clear Politics, and by 29 points in Iowa. But with the help of that single-digit margin in New Hampshire, he’s established himself as a clear number two: While rumors still swirl about a possible Joe Biden candidacy, Sanders is well ahead of him in all recent national polls.

On Sunday, 28,000 Sanders supporters filled an NBA arena in Portland, Oregon — the largest rally any 2016 presidential candidate has drawn so far. And Sanders proudly proclaims that his 284,000 individual contributors — more than Clinton’s 250,000 — gave an average of $31 each. “I ain’t gonna have a super PAC, I don’t need billionaires,” he said Monday. “This is a people’s campaign.”

Even those who strongly disagree with him tend to acknowledge that Sanders means what he says, slaking many Democrats’ thirst for genuineness.

Sanders is easily distinguished from “the more conventional establishment politician who is consistently hedging, and also begging for funding from major sources,” said Jack Citrin, director of the Institute of Governmental Studies at UC Berkeley. “He does have this authenticity, this down-home quality.”

He’s attracting those who are “dissatisfied and unhappy with the centrist positions that seem to dominate when it comes to nominating a presidential candidate,” Citrin said, nudging Clinton — who rolled out her own college-affordability plan Monday in Iowa — to adopt more liberal stances. “In his absence, she probably would have done some of that as well … but you could safely say he has been a goad on that front.”

Some liberals believe Clinton’s polished, conventional campaign is too deep in Wall Street’s pocket for her to stand up for ordinary working people. Hence Sanders’ rise as a conscience-of-the-party alternative: An NBC/Wall Street Journal poll conducted July 26-30 found that while 42 percent of registered voters said Clinton is hurting the Democratic Party’s image, only 9 percent said Sanders is.

National Nurses United’s 185,000-strong membership is heavily female, making its endorsement of Sanders a more significant shot across Clinton’s bow. Sanders said Monday that women will support whomever is best prepared to take on billionaires and Wall Street, fight for children’s care and education, and protect women’s and other groups’ rights.

The GOP is delighted to see anyone sap Clinton’s support. “As Bernie Sanders continues surging in the polls and Hillary Clinton’s trustworthy numbers plummet, it’s no surprise that more and more Democrats are excited for an alternative to Clinton and her scandal-plagued candidacy,” Republican National Committee spokesman Ninio Fetalvo said Monday.

And nobody at Wednesday’s event wanted to hear the conventional wisdom that Sanders can win neither the Democratic nomination nor a general election. He’s “calling out the damage that Wall Street has done to Main Street,” said Kelly Williams, a nurse watching from Massachusetts. “Bernie speaks truth to power.”

Josh Richman covers politics. Follow him at Twitter.com/Josh_Richman. Read the Political Blotter at IBAbuzz.com/politics.