WASHINGTON - Sen. Bernie Sanders, a Vermont Independent who supports socialist policies, lifted off his long-shot bid Thursday for the 2016 Democratic presidential nomination by declaring war on the "billionaire class" that he contends runs the political system.

In an address on the Capitol lawn, Sanders laid out an agenda that took aim at major conservative donors to Republican causes, but also landed subtle jabs on the Democratic front-runner, Hillary Rodham Clinton, a former secretary of state whose political ties to Wall Street have left some liberals yearning for an alternative.

"I don't believe that the men and women who defended American democracy fought to create a situation where billionaires own the political process," Sanders told reporters. "That's a huge issue."

He cited his opposition to the Iraq war, when he was a member of the House in 2002 and then-Sen. Clinton (N.Y.) supported the conflict, as well as his staunch opposition to an emerging trade deal with a dozen Pacific Rim nations that had its initial phases negotiated when Clinton served as the nation's top diplomat.

His main rhetorical targets were David and Charles Koch, industrialist brothers who have become political bogeymen for liberals because of their vast political spending. But Sanders suggested that it was valid to raise questions about the Clinton Foundation, which has come under scrutiny for accepting foreign donations.

"The issue here is not the Clinton Foundation - that's a fair issue - the issue is the huge amount of money that it takes to run a campaign today," he said.

The event was as unusual as Sanders, 73, with flowing white hair that evokes an image more in line with a New England professor than a presidential contender. Technically, Sanders had announced his candidacy in an e-mail to supporters earlier Thursday, so this was just a chance for him to lay out an agenda.

He is the longest-serving independent in Congress, first winning a House seat in 1990 and refusing to formally join the Democratic Party, even as he caucused with Democrats in both chambers. Now seeking that party's highest calling, he rejected any sense that he would register with the party now.

The contrast between Sanders and Clinton is stark, and his candidacy - especially his presence in the expected primary debates this fall - threatens to remind base Democrats why they may have pause supporting Clinton. The comparisons are plenty: Sanders' authenticity and hot, unvarnished rhetoric to Clinton's careful script; his unabashedly liberal agenda to her years of triangulation; his grassroots, small-donor campaign to her paid army of staffers and super-PAC allies.

On Thursday afternoon, Clinton said via Twitter, "I agree with Bernie. Focus must be on helping America's middle class. GOP would hold them back. I welcome him to the race. - H."

Sanders has impressed liberal activists in his visits to early caucus and primary states. In South Carolina last weekend, he fired up delegates at the state Democratic Party's annual convention and drew a standing ovation with his impassioned assault on the "billionaire class." He warned that the United States was becoming "an oligarchic form of society."

With the media and many Democratic activists hungry for a competitive primary, Sanders is banking on gaining notice through the news media.

The danger for Clinton is that, because of her dominance at the outset of the race, any surge by Sanders or another challenger in the polls could be interpreted as a sign that she was no longer the immutable, presumptive nominee.

The Sanders campaign believes it can raise about $50 million to wage a credible primary campaign and fund TV ads in the early states. It expects much of that money to come online from the deep network of small-dollar donors Sanders has built over his years in the Senate.

Sanders hopes to use his lack of a super PAC to his advantage, making the Citizens United court decision - which made it easier to spend unlimited funds on elections - a centerpiece of his populist message.

His campaign will be based in Burlington, Vt., and he hopes to have a staff by May.

Sen. Bernie Sanders

Born: Sept. 8, 1941, Brooklyn, N.Y.

College: B.S., University of Chicago, 1964.

Political career:

Mayor of Burlington, Vt., 1981-89.

Member, U.S. House of Representatives, Independent

from Vermont, 1991-2007.

U.S. senator, Independent

from Vermont, 2007-present.

- McClatchy NewspapersEndText