Vermont Sen. Bernie Sanders announced Thursday he is running for president, giving Hillary Clinton her first official Democratic primary challenger. 

At a press conference, the independent senator and self-described "democratic socialist" said he is "running to win," though he faces long odds against Clinton's juggernaut political operation -- and several other potential Democratic candidates. 

Sanders, in throwing his hat into the ring, urged the media to discuss “serious issues” and not turn the race for the White House into a soap opera. The white-haired populist preacher said America should refocus on income inequality and jobs. He also took a jab at political activist billionaires Charles and David Koch.

Sanders plans to hold an official launch on May 26 in Burlington, Vt. In an interview earlier with The Associated Press, Sanders promised to fight what he deems "obscene levels" of income disparity and a campaign finance system that is a "real disgrace."

“After a year of travel, discussion and dialogue, I have decided to be a candidate for the Democratic nomination for president," Sanders said in an email to his supporters. "But let's be clear. This campaign is not about Bernie Sanders. It about a grassroots movement of Americans standing up and saying: ‘Enough is enough. This country and our government belong to all of us, not just a handful of billionaires

In the email, he says billionaires are rigging the political system and that the U.S. is facing enormous challenges.

“The disastrous decisions of the Supreme Court in the Citizens United case and in other related cases are undermining the very foundations of American democracy, as billionaires rig the system by using their Super PACS to buy politicians and elections."

"People should not underestimate me," Sanders told The Associated Press.. "I've run outside of the two-party system, defeating Democrats and Republicans, taking on big-money candidates and, you know, I think the message that has resonated in Vermont is a message that can resonate all over this country."

As he has for months in prospective campaign stops in the early voting states, and throughout his political career, the former mayor of Burlington on Wednesday assailed an economic system that he said has devolved over the past 40 years and eradicated the nation's middle class.

Bernie Sanders to Announce Candidacy | InsideGov

"What we have seen is that while the average person is working longer hours for lower wages, we have seen a huge increase in income and wealth inequality, which is now reaching obscene levels," Sanders told the AP.

The son of an immigrant from Poland who sold paint for a living in Brooklyn, Sanders has for decades championed working-class Americans. He lost several statewide races in the 1970s before he was elected mayor of Burlington in 1981, and went on to represent Vermont in the U.S. House for 16 years before his election to the Senate in 2006.

An independent in the Senate, he caucuses with Democrats in Washington and he is likely to attract some interest from voters who have unsuccessfully sought to draft Massachusetts Sen. Elizabeth Warren to join the race.

But Sanders rejected the idea his appeal is limited to voters on the left, boldly predicting Wednesday that his message would appeal to both fellow independents and Republicans.

Sanders said he would release "very specific proposals" to raise taxes on wealthy Americans and corporations, as well as offer tuition-free education at all public colleges and universities. He touched on his past opposition to free-trade agreements, his support for heavier regulations of the Wall Street and the nation's banking industry, and his vote against the Keystone XL oil pipeline as a preview of his campaign.

"So to me, the question is whose views come closer to representing the vast majority of working people in this country," Sanders said. "And you know what? I think my views do."

The 73-year-old Sanders starts his campaign as an undisputed underdog against Clinton.

Sanders said he has known the former first lady, senator from New York and secretary of state for more than two decades. "I respect her and like her," he said.

He noted he has "never run a negative ad in my life," but still drew a distinction with Clinton in the interview, promising to talk "very strongly about the need not to get involved in perpetual warfare in the Middle East."

"I voted against the war in Iraq," he said. "Secretary Clinton voted for it when she was in the Senate."

Clinton is hosting a series of fundraisers this week, starting what could be an effort that raises more than $1 billion. Sanders said he will make money and politics a central theme of his campaign, including a call for a constitutional amendment to overturn the U.S. Supreme Court's 2010 Citizens United decision, which he blames for unleashing a torrent of money from wealthy donors into politics.

Sanders is the first major challenger to enter the race against Clinton, who earlier this month became the first Democrat to formally declare her intention to run for president. He is likely to be joined in the coming months by former Maryland Gov. Martin O'Malley, former Virginia Sen. Jim Webb and ex-Rhode Island Gov. Lincoln Chafee.

The Associated Press contributed to this report