“Don’t underestimate me,” declared newly announced presidential candidate Bernie Sanders to George Stephanopoulos on Sunday. That may be good advice.

By conventional standards, Sanders’s candidacy is absurd: He’s not well known, he doesn’t have big money donors, he’s not charismatic, and by Beltway standards, he’s ideologically extreme. But candidates with these liabilities have caught fire before. Think of Jerry Brown, who despite little funding and an oddball reputation outlasted a series of more conventional candidates to emerge as Bill Clinton’s most serious challenger in 1992. Or Pat Buchanan, who struck terror in the GOP establishment by winning the New Hampshire primary in 1996. Or Howard Dean, who began 2003 in obscurity and ended it as the Democratic frontrunner (before collapsing in the run-up to the Iowa Caucuses). Or Ron Paul, who in 2012 finished second in New Hampshire and came within three points of winning Iowa.

What did all these insurgents share? They gave authentic voice to the grievances of their time. In the wake of a congressional banking scandal and a congressional pay hike, Brown vowed to take “take back America from the confederacy of corruption, careerism, and campaign consulting in Washington.” In an era of escalating globalization, Buchanan promised a “conservatism that looks out for the men and women of this country whose jobs have been sacrificed on the altars of trade deals done for the benefit of trans-national corporations who have no loyalty to our country.” In a Democratic Party whose activists felt betrayed by their leaders’ support for the Iraq War, Dean pledged “to represent the Democratic wing of the Democratic Party.”

In today’s Democratic Party, the most powerful grievance is the one that brought thousands into Zuccotti Park in 2011, powered Bill De Blasio’s upset victory in New York, and has made Elizabeth Warren a progressive folk hero. It’s the belief that the super-rich have distorted America’s economy and bought its government. It’s a grievance so powerful that it’s seeped not only into Hillary's rhetoric, but also into Ted Cruz's. And from the Clinton Foundation scandals to the Republican candidates’ shameless pandering to billionaires, the presidential campaign itself seems poised to inflame that grievance even more.

Sanders is better positioned to exploit this resentment against the one percent that many pundits understand. First, because he’s virtually the only Democrat challenging Hillary (especially given the Baltimore riots’ crippling impact on Martin O’Malley) Sanders will get more media attention than he would in a more crowded field. Second, although Hillary Clinton has shifted left, her ties to Wall Street—and her need to raise vast sums from it—will keep her from fully assuaging the party’s left. Three weeks into her presidential bid, for instance, she still hasn’t taken a clear position on either the Keystone Pipeline or fast-track authority for the Trans-Atlantic and Trans-Pacific trade deals, even though progressive activists loathe both. Third, there today exists a liberal media echo-chamber—from MSNBC to MoveOn to Daily Kos—that did not exist in the 1990s, and which amplifies whoever in the Democratic Party articulates the most ambitious, most uncompromising progressive agenda.

Fourth, while Sanders lacks Warren’s charisma—he’s the Eugene McCarthy to her Robert Kennedy—he shares a key quality with the successful insurgents of the past: authenticity. Like Ron Paul, he has held firm to his ideological convictions for decades, despite the mockery of the political mainstream. And he articulates those convictions bluntly and without artifice. Asked to explain why they’re running for president, mainstream candidates often retreat into safe, Hallmark-card platitudes. Sanders, by contrast, told Stephanopoulos, “I’m the only candidate who is prepared to take on billionaire class which controls our economy and increasingly controls the political life of this country.” When Sanders said Scandinavia best exemplifies his brand of democratic socialism, Stephanopoulos tried to brush him back: “I can hear the Republican attack ad right now: He wants America to be look more like Scandinavia.” But Sanders was not cowed. “That’s right. That’s right,” the Vermont senator replied. “And what’s wrong with that? What’s wrong when you have more income and wealth equality? What’s wrong when they have a stronger middle class in many ways than we do?”

Do most Americans want our economic system to look like Scandinavia’s? Maybe not. But many liberal Democrats do. And even more importantly, many liberal Democrats want a candidate who won’t compromise his beliefs because they transgress Beltway conventional wisdom. That’s why so many rallied behind Dean, and that refusal will be core to Sanders’s appeal as well.

I don’t think Sanders can beat Hillary, in part because I doubt he can cut into her support among Latinos and African Americans. But he can scare her. As Dean and Paul showed, candidates without wealthy backers can raise large sums via small donations on the web, thus win respectability from the mainstream press. Sanders has a long way to go. But as Peter Weber has noted, he raised $1.5 million from 35,000 people on the first day of his campaign, more than any of the Republican candidates did in the 24 hours after they announced.

The day Sanders announced he was challenging Hillary, Jon Stewart commented that, “He has a set of consistent principles that he has run on his entire political life. She is going to crush him.” Right now, in other words, Stewart—and most other progressives—see Sanders as one-part admirable, three-parts absurd. If that balance starts to tip, the 2016 Democratic primary may become a lot more interesting than anyone expects.