U.S. Sen. Bernard Sanders (I-VT) speaks on his agenda for America during a news conference on Capitol Hill. (Photo by Alex Wong/Getty Images)

This story has been updated.

Sen. Bernie Sanders (I-Vt.) officially launched his bid for the Democratic nomination Thursday, calling in a press conference outside the Capitol for "an economy that works for all of our people, rather than a small number of billionaires."

"Ninety-nine percent of all new income generated in this country is going to the top 1 percent. How does it happen that the top 1 percent owns almost as much wealth as the bottom 90 percent?" he told reporters. "My conclusion is, that that type of economics is not only immoral, it is not only wrong, it is unsustainable."

The self-described socialist, known for his blunt style, enters the race as a progressive favorite eager to push presumed Democratic front-runner Hillary Clinton to the left. Asked what made him a better candidate than Clinton, he first sidestepped the question -- "we don't know what Hillary's stances are on all the issues" -- before highlighting issues where he's taken a progressive leadership role, including opposition to the Trans-Pacific Partnership trade agreement, the Keystone XL pipeline, and the Iraq War.

"I voted against the war in Iraq," he said -- drawing a contrast with Clinton, whose vote in favor of the war helped sink her 2008 presidential campaign.

The Post’s Robert Costa and Dan Balz reported on Sanders’ imminent presidential run Tuesday after several key allies made it clear he would seek the Democratic nomination:

Sanders presents a notable left-leaning challenge to Hillary Rodham Clinton, the front-runner for the Democratic presidential nomination, who announced her second campaign for the White House on April 12. …

Sanders shares many of the same political stances as Sen. Elizabeth Warren (D-Mass.), a darling of liberals who has repeatedly said she is not running for president. That means Sanders may end up serving as the most prominent voice for the left wing of the party — particularly voters who are suspicious of Clinton and her ties to Wall Street. …

Sanders chose to run in the Democratic primary because of to his interest in participating in the party’s primary debates, according to confidants. If he ran as an independent, he would not be able to engage with the national Democratic infrastructure or act as a direct foil to Clinton in the early primaries and caucuses.

Sanders spoke Thursday about several key progressive issues that will frame his campaign, including income inequality and unemployment, campaign finance reform, education reform and climate change.

“I believe that in a democracy what elections are about are serious debates over serious issues -- not political gossip, not making campaigns into soap offices. This is not the Red Sox versus the Yankees,” he said. “I would hope -- and I ask the media's help on this -- allow us to discuss the important issues facing the American people."

And the long-shot contender denied that he was in the race merely to draw attention to issues he cares about. "We're in this race to win," he insisted.

Sanders on Saturday will head to New Hampshire, which host's the nation's first presidential primary, where he will attend a house party with supporters and address an AFL-CIO convention. He is expected to hold a rally in his home state of Vermont next month.