{{show_title_date || "Full video: Bernie Sanders announces presidential bid, 4/30/15, 12:38 PM ET"}}

Bernie Sanders: ‘I am running for president of the United States’

Updated

Hillary Clinton officially has some competition for the Democratic presidential nomination.

Independent Vermont Sen. Bernie Sanders formally announced his candidacy on Thursday, tweeting “I am running for president of the United States because America needs a political revolution.”

Shortly afterward, Sanders, 73, held a press conference in Washington D.C., where he struck a populist tone and laid out a policy agenda that included economic inequality, climate change and ending big money in politics.

“All over this country, I’ve been talking to people — 99% of all new income generated in this country is going to the top 1%. How does it happen that the top 1% owns almost as much wealth as the bottom 99%?” said Sanders, who is the longest-serving independent in Congressional history. He also knocked Republicans for failing to recognize the “reality of climate change, let alone that it is caused by human activity.”

The senator boasted that he’d never run a negative ad “in my life” and was asked whether scrutiny over Clinton’s possible conflicts of interest relating to her family foundation was fair. Sanders said yes, but added, “What is more fair game is the role of money in politics.”

RELATED: Who will be Hillary Clinton’s chief Democratic rival?

A self-described “Democratic socialist,” Sanders is largely considered a long-shot for the party’s nomination but is also being viewed as a liberal alternative to Clinton, who some believe is too centrist. His entry could mean Clinton will be pushed to talk more about critical issues that the progressive wing of the party cares about, like income inequality.

When asked to distinguish himself from the former secretary of state, Sanders pointed out that he voted against the war in Iraq, while Clinton voted in favor of it when she was senator. Sanders also pointed out that he has been against the controversial Keystone XL pipeline, which would create an oil transport system from Canada to the Gulf of Mexico. So far, Clinton has largely sidestepped the issue.

Although Sanders is an independent, he’s running as a Democrat because it will be easier to get his name on the ballot in all 50 states.

“The reason is pretty simple,” he told msnbc’s Andrea Mitchell. “I’m not a billionaire. To run outside of the two-party system would require enormous sums of money and a great expenditure of energy and time just to get on the ballot.”

Sanders is expected to travel to the early voting state of New Hampshire on Saturday. 

Clinton welcomed Sanders to the race via Twitter on Thursday. “I agree with Bernie. Focus must be on helping America’s middle class. GOP would hold them back,” she tweeted on her campaign account.

Afterwards, Sanders tweeted back: “Thanks @HillaryClinton. Looking forward to debating the big issues: income inequality, climate change & getting big money out of politics. “

Bernie Sanders and Hillary Clinton

Bernie Sanders: 'I am running for president of the United States'

Updated