Independent Vermont Senator Bernie Sanders on Wednesday confirmed earlier reports he will run for president as a Democrat, The Associated Press (AP) reported.

Speaking to the news agency, Sanders promised to fight what he deems “obscene levels” of income disparity and a campaign finance system that is a “real disgrace”.

Sanders added that he plans to formally join the race Thursday.

The self-described “democratic socialist” enters the race as a robust liberal alternative to Hillary Clinton, and he pledged to do more than simply raise progressive issues or nudge the former secretary of state to the left in a campaign in which she is heavily favored.

“People should not underestimate me,” Sanders told AP. “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.”

The former mayor of Burlington, Vermont, assailed an economic system that he said has devolved over the past 40 years and eradicated the nation’s middle class.

“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 AP.

“This is a rigged economy, which works for the rich and the powerful, and is not working for ordinary Americans. … You know, this country just does not belong to a handful of billionaires,” he added.

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

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 told AP.

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.”

Sanders, who is Jewish, recently made headlines when he became the first senator to announce he would not be attending Prime Minister Binyamin Netanyahu’s speech before Congress.

“The president of the United States heads up our foreign policy. The idea that the president wasn’t even consulted — that is wrong and not a good thing for our country,” Sanders said at the time, referring to the fact that House of Representatives Speaker Republican John Boehner invited Netanyahu to make the speech without the knowledge of either the White House’s or Democratic leaders in Congress.

“I’m not thinking about it. I’m not going. I may watch it on TV,” Sanders stressed.