Sen. Bernie Sanders on Tuesday announced he's running for president in 2020.

Sanders' 2016 presidential campaign made him a household name, even though he lost the Democratic primary to former Secretary of State Hillary Clinton.

The ghosts of the 2016 primary season may continue to haunt Sanders in 2020, but he also remains one of the most popular US politicians.

Sen. Bernie Sanders of Vermont on Tuesday announced he's running for president in 2020.

Sanders, an independent who caucuses with the Democrats, ran for the Democratic presidential nomination in 2016. Though he lost to former Secretary of State Hillary Clinton, his campaign took him from being a relatively obscure political figure to a household name.

In an official announcement video released Tuesday, Sanders launched into some of his best-known arguments, including the ideas that the US economy is "rigged" and that "nobody in America who works 40 hours a week should be living in poverty."

The video includes clips of town and city life in America and footage from his 2016 presidential bid. It shows news footage of policies backed by Sanders gaining popularity in the US — such as Medicare expansion, free college tuition, and the addressing of income inequality.

It also shows footage of Sanders on the Women's March and speaking out President Donald Trump's immigration policies. It also highlights Sanders' campaign to force Amazon to increase wages.

"Brothers and sisters, we have a lot of work in front of us," Sanders says in the video. "If we are prepared to stand together, there is no end to what the great people of our nation can accomplish."

According to a campaign email Tuesday, Sanders will launch a multistate tour "in the next few weeks" to "share his vision to transform the country for the many, not the few."

"I am asking you to join me today as part of an unprecedented and historic grassroots campaign that will begin with at least a million people from across the country," he said in the email to supporters.

In an interview with Vermont Public Radio (VPR) early on Tuesday morning, Sanders said, "We began the political revolution in the 2016 campaign, and now it's time to move that revolution forward."

"I wanted to let the people of the state of Vermont know about this first," Sanders told VPR. "And what I promise to do is, as I go around the country, is to take the values that all of us in Vermont are proud of—a belief in justice, in community, in grassroots politics, in town meetings—that's what I'm going to carry all over this country."

Sanders' 2016 campaign shocked much of the country, as few expected him to pose a significant challenge to Clinton at the start. But his populist platform and matter-of-fact style of speaking, along with his thick Brooklyn accent, won over a significant cohort of voters.

The Vermont senator was especially popular with young voters in 2016, garnering more votes from this demographic than the two major-party presidential nominees combined.

But he struggled to win over the Democratic establishment, and many dismissed his policy proposals as idealistic and unrealistic.

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Some of Sanders' supporters accused the Democratic National Committee of rigging the primaries in Clinton's favor and robbing the election from him, though there's no concrete evidence to support this notion.

After a heated primary season, Sanders supported Clinton in her effort to defeat Trump in the general election. Some Clinton supporters felt he should've conceded and dedicated his support to her earlier in the campaign season, pointing to Sanders as one of the reasons she lost the general election.

Some of these issues could haunt Sanders along the campaign trail in the coming presidential election, on top of sexual-harassment allegations involving members of his campaign.

Read more: Bernie Sanders campaign alumni want to address the sexual harassment they say took place in 2016 as he mulls another presidential run

The allegations were not directed at Sanders, but several women who worked on the campaign said they were harassed by staff members and also experienced pay disparities. Sanders has apologized for this, saying he was not aware of the allegations amid the campaign season.

Despite some of the obvious challenges Sanders will face moving forward, he remains one of the most popular politicians in the country.