AMES, Iowa » Sen. Bernie Sanders, an independent from Vermont who calls himself a socialist, was riding in the back seat of a rented blue minivan this week when his aide abruptly announced they were being pulled over by the Iowa State Police for speeding.

"Hi ya, I’m Senator Bernie Sanders, how ya doing?" Sanders piped up, in his unmistakable Brooklyn accent, after the aide explained to the police officer that they were late for the senator’s appearance here.

The officer issued no ticket, just a warning to slow down: "No need making a headline for something silly."

Sanders, though, was in Iowa hoping to make headlines. At 73 and famously gruff, he may be on one of the most quixotic adventures in U.S. politics: In a country that just put Republicans in charge of Congress, he is testing whether Democrats will embrace a socialist for the White House in 2016. He is certainly the only potential candidate to carry a brass key chain from a campaign of Eugene V. Debs, a five-time Socialist Party nominee for president.

He has virtually no chance of winning the nomination, but he does have a chance to shape the debate — presuming he actually runs. With his fiery populist attacks on Wall Street and "the billionaire class," he could become either a nettlesome thorn to Hillary Rodham Clinton or a convenient foil for her, if she runs.

"Sanders could become the vessel for the anger of the Democratic left," said David Yepsen, a longtime Iowa political reporter who now directs a public policy institute at Southern Illinois University. "Now that Democrats are searching for a nominee, how liberal are they going to be? And the fact that he’s a little quirky could almost have some appeal."

Here in Ames, that much was clear at least among the crowd of 250 college students, liberal activists and retirees who packed a church basement to hear Sanders. Using a milk crate as a podium, he delivered the kind of tirade for which he is well known in Washington. He did not mention his encounter with the police officer.

He railed against big banks ("Break ’em up!"), fretted over climate change and income inequality, and deplored the high cost of a college education ("Totally moronic."). He embraced a single-payer health system ("Guess what everybody! Health care is a right!"), proposed strengthening labor unions and lamented a lack of voter participation ("All over this country people are throwing up their hands in despair.").

But Sanders reserved his greatest ire for what he called "one extreme right-wing billionaire family," the brothers Charles and David Koch. In his view, they are the root of what is wrong in U.S. politics.

"The Koch brothers are worth $85 billion. You might think that’s enough to get by, leave a couple of bucks to your kids," the senator thundered, his voice rising, face reddening. "But apparently they feel an obligation to destroy Social Security, Medicare and Medicaid."

The crowd lapped it up.

"We need a debate in the Democratic Party about where we’re going," said Sandy Easter, a 65-year-old alternative healer and homeopath who distributed "Run, Bernie, Run" stickers. "I think he’s folksy — the real thing."

But quirky and folksy can take a candidate only so far, and Sanders is hardly without liabilities. For starters, there is the socialist label.

"That’s something that Bernie is going to have to overcome," said Democratic strategist Tad Devine, who is advising Sanders. "He is going to have to convince people he is a serious, credible candidate."

Sanders will turn 75 in 2016. After three decades in public office, he cannot exactly market himself as new or fresh, like Barack Obama did in 2008 or Sanders’ fellow Vermonter Howard Dean (who has endorsed Clinton) did in 2004.

And Sanders has competition: Liberal groups like MoveOn.org are mounting a campaign to draft a populist with a far larger national following, Sen. Elizabeth Warren of Massachusetts, even though she insists she is not running.

On a recent morning in the Capitol, the two senators could be found in opposite corners of the private Senate dining room. Over a Vermont-worthy breakfast of yogurt with granola and berries (with a touch-of-Brooklyn English muffin on the side), Sanders called Warren a friend and said he had discussed his intentions with her.

"Private conversation," he said, waving off questions about specifics.

Pressed on whether he would run if she did, he flashed his prickly side.

"Look," he said, "Elizabeth is over there. You want to talk to her? Go talk to her."

With his socialist leanings and unruly shock of white hair that evokes mad scientist references on Twitter, people think Sanders ought to be funny, but he is stone-cold serious. That trait earns him respect in the Senate but could give his campaign a mandatory seminarlike quality.

"He seems rather humorless," said Michael Kazin, a Georgetown University historian who wrote in The New Republic this spring that a Sanders run would be good for Democrats.

Dean has a different take.

"Bernie actually does have a sense of humor," he said. "But I would agree it’s well concealed."

The son of a Polish-born paint salesman who "came to this country without a nickel in his pocket," Sanders grew up listening to his parents fight about money, a fact that he says shaped his political views. He says wryly that "unlike, historically, most of my colleagues in this institution," the Senate, he does not wake up each morning with visions of the Oval Office.

"I honestly believe anybody who really, really wants to become president is a little bit crazy," he said, "because the problems facing this country and the world are so overwhelming."

He wonders if he is the man who can solve them. So a few months ago, he had a heart-to-heart with Devine, who has advised him in previous races.

Devine said Sanders should not be underestimated; he raised $8 million for his 2012 election, without a serious opponent, and still has nearly $4.5 million in the bank. He has enthusiastic followers on Facebook and Twitter.

But in order to avoid being dismissed as a gadfly, Devine said he told the senator that he would have to raise about $50 million, presumably through small online contributions. Not only that, he would have to build a ground operation in states like Iowa and New Hampshire and run as a Democrat to avoid being seen as a spoiler.

"He is going to have to convince millions of people that he’s got a real candidacy," Devine said.

Thus the trip to Iowa, Sanders’ fourth visit to the state this year. He has also been to California, New Hampshire, South Carolina, and Mississippi — part of an effort, he said, to figure out if he can indeed recruit millions into an "unprecedented grass-roots campaign." He said he will decide over the next few months, based on "gut reaction," if he should run.

Matthew Covington, an organizer for the Iowa Citizens for Community Improvement Action Fund, which has been hosting events for Sanders around the state, said he hoped Sanders would. After the event in Ames, Covington said Sanders was "laying out ideas and policy proposals that resonate with a lot of people."

But could he win? Covington looked stricken at the question and buried his face in his hands.

"Can I not answer that?" he asked.

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