The independent Vermont senator railed against the political machine — blasting "ugly 30-second ads," billionaire big-money donors and other "soap opera aspects of modern campaigns" — in a press conference kicking off his candidacy outside the Capitol on Thursday.

"I think the American people are tired of that," Sanders said.

He said he is running to thwart trade deals like the 12-country Trans-Pacific Partnership and to overhaul business tax rules so corporations operating in the United States cannot shelter their money overseas.

"Their responsibilities are not to shift jobs to China, their responsibility is not to avoid paying federal taxes," he said.

Sanders first announced his run in an email to supporters and media sent just after midnight early Thursday morning.

"After a year of travel, discussion and dialogue, I have decided to be a candidate for the Democratic nomination for president," he wrote in the email, highlighting economic inequality, climate change and the Citizens United Supreme Court decisions as key issues spurring him to run.

Sanders first confirmed to the Associated Press in a story published Wednesday that he plans to run for the Democrats' 2016 presidential nomination.

"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."

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Sanders caucuses with the Democrats in the Senate but is an unlikely candidate for the Democratic nomination, primarily because he has never been a registered member of the party and calls himself a "democratic socialist."

Yet many of his views fit with the Democratic left, a constituency in which Sanders has found a small yet devout following. Sanders and his top advisers hope that group of voters will propel his dark horse candidacy. Though Hillary Clinton is the dominant frontrunner, many in the progressive left of the party think she's too moderate and are clamoring for a different candidate to support.

For their part, the Democratic National Committee offered a measured welcome of Sanders to the 2016 race on Thursday.

"Sanders is well-recognized for his principled leadership and has consistently stood up for middle class families," DNC Chairwoman Debbie Wasserman Schultz said in the statement. "Throughout his service in the U.S. House and Senate, Bernie Sanders has clearly demonstrated his commitment to the values we all share as members of the Democratic Party."

Sanders' campaign advisers said that while their candidate has announced his plans to run, he won't hold his first campaign rally until May. That event is expected to be in Vermont.

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Sanders is an outspoken critic of Wall Street banks and the outsized influence of money in politics and is a supporter of universal health care. He regularly talks about the need to rebuild the middle class and raise taxes on America's highest earners.

"At a time of massive wealth and income inequality, we need a progressive tax system in this country which is based on ability to pay," Sanders said last month in Washington. "It is not acceptable that a number of major profitable corporations have paid zero in federal income taxes in recent years, and that millionaire hedge fund managers often enjoy an effective tax rate which is lower than the truck drivers or nurses."

In interviews before his campaign announcement, Sanders said trade, income inequality and health care would be key tenants of his run. But despite having vocal liberal supporters on these issues, Sanders is a dark horse candidate and has acknowledged that his run will be uphill. A CNN/ORC poll in March found that Sanders has the support of only 3% of Democratic voters.

Born in Brooklyn, New York, Sanders moved to Vermont after graduating from the University of Chicago. His first successful run for office came in 1981 when he was elected Burlington's mayor by a mere 10 votes. He was elected as Vermont's at-large member of Congress in 1990 and jumped to the Senate in 2007. Sanders is the longest-serving independent in congressional history.

Sanders does not have the personality of a typical politician. He is sometimes gruff and blunt, dispensing with social niceties and usually getting right to the point. He has come to be known as much for his fly-away hair as his passionate speeches in the Senate -- and has bluntly lamented the way political journalism in the United States focuses on personality.

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"I think this is not about personality," Sanders told CNN earlier this year, raising his Vermonter-by-way-of-New York voice. "I am not a singer, I am not a dancer, I am not an entertainer."

He also starts with a small campaign infrastructure, largely the remnants of his past Senate runs, and is primarily being advised by Tad Devine, a Democratic political consultant who worked on the presidential campaign for Al Gore in 2000 and John Kerry in 2004. At an event this month in New Hampshire where Sanders leaned heavily into a presidential bid, the signs outside the house party touted his 2012 Senate re-election bid.

From the outset of his campaign, it appears money will be Sanders' biggest issue. The senator has regularly conceded in the last month that he would not be able to raise near the money Clinton will bring in.

"To run a credible campaign in this day and age, you do need a whole lot of money," Sanders said. "Whether the magic number is $200 million, it is $150 million, it is a lot of money, but even with that, you would be enormously outspent by the Koch Brother candidates and the other candidates who will likely spend, in the final analysis, over $1 billion, if not two."

Despite being a champion for many on the left, Sanders has been somewhat left out in the cold by big liberal organizations like MoveOn.org and Democracy for America, who have spent the last few months unsuccessfully urging Massachusetts Sen. Elizabeth Warren to run for president.

"Obviously one would hope one would have as much support as possible from all walks of life," Sanders said on Tuesday when asked why he thinks those groups aren't rallying around him. "I am a great fan of Elizabeth and as for what people do and why they don't do it, I am not going to speculate."

Photos: Potential 2016 presidential candidates Photos: Potential 2016 presidential candidates Former Florida Gov. Jeb Bush has said his decision to run for the Republican nomination will be based on two things: his family and whether he can lift America's spirit. His father and brother are former Presidents. Hide Caption 1 of 19 Photos: Potential 2016 presidential candidates Wisconsin Gov. Scott Walker has created a political committee that will help him travel and raise money while he considers a 2016 bid. Additionally, billionaire businessman David Koch said in a private gathering in Manhattan this month that he wants Walker to be the next president, but he doesn't plan to back anyone in the primaries. Hide Caption 2 of 19 Photos: Potential 2016 presidential candidates Louisiana Gov. Bobby Jindal is establishing a committee to formally explore a White House bid. "If I run, my candidacy will be based on the idea that the American people are ready to try a dramatically different direction," he said in a news release provided to CNN on Monday, May 18 Hide Caption 3 of 19 Photos: Potential 2016 presidential candidates Sen. Bernie Sanders , an independent from Vermont who caucuses with Democrats, has said the United States needs a "political revolution" of working-class Americans looking to take back control of the government from billionaires. He first announced the run in an email to supporters early on the morning of Thursday, April 30. Hide Caption 4 of 19 Photos: Potential 2016 presidential candidates On March 2, retired neurosurgeon Ben Carson announced the launch of an exploratory committee. The move will allow him to raise money that could eventually be transferred to an official presidential campaign and indicates he is on track with stated plans to formally announce a bid in May. Hide Caption 5 of 19 Photos: Potential 2016 presidential candidates South Carolina Sen. Lindsey Graham has said he'll make a decision about a presidential run sometime soon. A potential bid could focus on Graham's foreign policy stance. Hide Caption 6 of 19 Photos: Potential 2016 presidential candidates Hillary Clinton launched her presidential bid Sunday, April 12, through a video message on social media. She continues to be considered the overwhelming front-runner among possible 2016 Democratic presidential candidates. Hide Caption 7 of 19 Photos: Potential 2016 presidential candidates Sen. Marco Rubio announced his bid for the 2016 presidency on Monday, April 13, a day after Hillary Clinton, with a rally in Florida. He's a Republican rising star from Florida who swept into office in 2010 on the back of tea party fervor. But his support of comprehensive immigration reform, which passed the Senate but has stalled in the House, has led some in his party to sour on his prospects. Hide Caption 8 of 19 Photos: Potential 2016 presidential candidates Lincoln Chafee, a Republican-turned-independent-turned-Democrat former governor and senator of Rhode Island, said he's running for president on Thursday, April 16, as a Democrat, but his spokeswoman said the campaign is still in the presidential exploratory committee stages. Hide Caption 9 of 19 Photos: Potential 2016 presidential candidates Jim Webb, the former Democratic senator from Virginia, is entertaining a 2016 presidential run. In January, he told NPR that his party has not focused on white, working-class voters in past elections. Hide Caption 10 of 19 Photos: Potential 2016 presidential candidates Vice President Joe Biden has twice before made unsuccessful bids for the Oval Office -- in 1988 and 2008. A former senator known for his foreign policy and national security expertise, Biden made the rounds on the morning shows recently and said he thinks he'd "make a good President." Hide Caption 11 of 19 Photos: Potential 2016 presidential candidates New Jersey Gov. Chris Christie has started a series of town halls in New Hampshire to test the presidential waters, becoming more comfortable talking about national issues and staking out positions on hot topic debates. Hide Caption 12 of 19 Photos: Potential 2016 presidential candidates Rep. Paul Ryan, a former 2012 vice presidential candidate and fiscally conservative budget hawk, says he's keeping his "options open" for a possible presidential run but is not focused on it. Hide Caption 13 of 19 Photos: Potential 2016 presidential candidates Sen. Rand Paul officially announced his presidential bid on Tuesday, April 7, at a rally in Louisville, Kentucky. The tea party favorite probably will have to address previous controversies that include comments on civil rights, a plagiarism allegation and his assertion that the top NSA official lied to Congress about surveillance. Hide Caption 14 of 19 Photos: Potential 2016 presidential candidates Texas Sen. Ted Cruz announced his 2016 presidential bid on Monday, March 23, in a speech at Liberty University. The first-term Republican and tea party darling is considered a gifted orator and smart politician. He is best known in the Senate for his marathon filibuster over defunding Obamacare. Hide Caption 15 of 19 Photos: Potential 2016 presidential candidates Democrat Martin O'Malley, the former Maryland governor, released a "buzzy" political video in November 2013 in tandem with visits to New Hampshire. He also headlined a Democratic Party event in South Carolina, which holds the first Southern primary. Hide Caption 16 of 19 Photos: Potential 2016 presidential candidates Republican Rick Perry, the former Texas governor, announced in 2013 that he would not be seeking re-election, leading to speculation that he might mount a second White House bid. Hide Caption 17 of 19 Photos: Potential 2016 presidential candidates Former Pennsylvania Sen. Rick Santorum, a social conservative, gave Mitt Romney his toughest challenge in the nomination fight last time out and has made trips recently to early voting states, including Iowa and South Carolina. Hide Caption 18 of 19 Photos: Potential 2016 presidential candidates Political observers expect New York Gov. Andrew Cuomo to yield to Hillary Clinton's run in 2016, fearing there wouldn't be room in the race for two Democrats from the Empire State. Hide Caption 19 of 19

Anna Galland, executive director of MoveOn.org Civic Action, even mentioned Warren in touting Sanders' jump into the race.

"MoveOn members welcome Sen. Bernie Sanders to the presidential race," said Galland. "The Democratic Party is made stronger by each additional voice who enters the race and commits to being a strong advocate for everyday, hardworking Americans and not just the wealthy few. That's why we and our allies continue to call on Sen. Elizabeth Warren to also bring her tireless advocacy for middle-class and working Americans to the race. Our country will be stronger if she runs."

Sanders enters a race that has so far been dominated by Clinton, the former secretary of state and Democrats' prohibitive favorite for the nomination. For most of 2015, Sanders has been reticent to attack Clinton, but he recently has issued statements calling on her to change her policy positions.