BURLINGTON, Vt. (AP) — Challenging Hillary Rodham Clinton from the left, Vermont Sen. Bernie Sanders formally launched his Democratic presidential campaign on Tuesday by vowing to start a "political revolution" to address core economic issues, massive student debt and the role of big money in politics.

Already in the race for the Democratic presidential nomination, Sanders was opening his campaign with a kickoff event — complete with free Ben & Jerry's ice cream — in Burlington, the place where he won his first election by beating a longtime incumbent Democrat by 10 votes to become mayor.

"I know what I believe," Sanders said in a fundraising email hours before his launch that pushed back against "the billionaire class" trying to buy the election. "That's why today marks the beginning of our political revolution."

Sanders, a self-described "democratic socialist," is trying to ignite a grassroots fire among left-leaning Democrats wary of Clinton — a group that pined for months for Massachusetts Sen. Elizabeth Warren to get in to race. Some still do.

But while Warren remains committed to the Senate, repeatedly saying she won't run for the White House, Sanders is laying out an agenda in step with the party's progressive wing and Warren's platform — reining in Wall Street banks, tackling college debt and creating a government-financed infrastructure jobs program.

"Hillary Clinton is a candidate. I am a candidate," Sanders said in an interview with The Associated Press. "I suspect there will be other candidates. The people in this country will make their choice."

Clinton is in a commanding position by any measure, far in front of both Sanders and former Maryland Gov. Martin O'Malley, who is widely expected to get into the race Saturday.

Yet Sanders' supporters in New Hampshire say his local ties and longstanding practice of holding town hall meetings and people-to-people campaigning — a staple in the nation's first primary state — will serve him well.

"Toward the Vermont border it's like a love-fest for Bernie," said Jerry Curran, an Amherst, New Hampshire, Democratic activist who has been involved in the draft Warren effort. "He's not your milquetoast left-winger. He's kind of a badass left-winger."

Sanders, an independent in the Senate who often votes with the Democrats, has raised more than $4 million since announcing in late April that he would seek the party's nomination. He suggested in the interview that raising $50 million for the primaries was a possibility. "That would be a goal," he said.

Whether Sanders can tap into the party's Warren wing and influence Clinton's policy agenda remains unclear. But he has been on the forefront of liberal causes as Clinton has seemed to be tacking to the left.

Clinton regularly refers to an economic stacked deck against American workers — rhetoric that offers comparisons to Warren's frequent description of the economic system being "rigged" against middle-class families.

Sanders joined with Warren to drive opposition to the Trans-Pacific Partnership trade proposal, arguing it would ship jobs overseas. Clinton has avoided taking a specific position on the trade deal.

He has introduced legislation to make tuition free at public colleges and universities, a major piece of Warren's agenda. Clinton's campaign has signaled that she intends to make debt-free college a major piece of her campaign.

Sanders' disdain for big money in politics is also shared by liberals. Clinton frequently tells voters that she would back a constitutional amendment to overturn the Supreme Court decision allowing super PACS to raise unlimited money. But Democratic super PACs are already lining up behind her.

"I'm not going to have a super PAC in this campaign," said Sanders, who has raised money from more than 100,000 individual donors, giving an average of $42 each.

If Sanders is the underdog, that's fine by him. During the 1970s, he lost four statewide elections as a third-party candidate, and then narrowly defeated a Democratic incumbent in 1981 to become Burlington's mayor.

"Nobody — trust me — nobody thought I would defeat a five-term incumbent Democratic mayor," Sanders said. The lessons, he said, are clear: "Don't underestimate me."

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