click to enlarge FILE: MORIAH HOUNSELL

Sen. Bernie Sanders campaigns in New Hampshire in May 2015.

click to enlarge File: James Buck

Sen. Bernie Sanders kicks off his first presidential campaign at the Burlington waterfront in May 2015.

click to enlarge File: Eric Tadsen

Sen. Bernie Sanders campaigns in July 2015 in Madison, Wis.

click to enlarge File: Paul Heintz

Sen. Bernie Sanders in Iowa in January 2016

Sen. Bernie Sanders (I-Vt.) will make a second run for the White House in 2020, he announced Tuesday morning.The senator disclosed his candidacy in an interview with Vermont Public Radio , telling host Bob Kinzel, “I wanted to let the people of the state of Vermont know about this first.”Sanders elaborated on his plans in an 11-minute video and a 1,500-word email to supporters, in which he sounded many of the populist, progressive themes that have characterized his nearly five decades in public life — and made him a breakout star of the 2016 presidential election. “Our campaign is about taking on the powerful special interests that dominate our economic and political life,” he said.Asked in a pre-taped interview with CBS News’ John Dickerson how this campaign would differ from his last, Sanders said, “We’re gonna win.”"Our campaign is not only about defeating Donald Trump, the most dangerous president in modern American history," Sanders said in his announcement. "Our campaign is about transforming our country and creating a government based on the principles of economic, social, racial and environmental justice."The 77-year-old independent joins a crowded Democratic field, which already features five other U.S. senators and is expected to include more than a dozen members of Congress, governors, mayors and business leaders. Sanders, however, is the highest-profile pol to enter the race thus far — and the only one to have previously sought the office. Only former vice president Joe Biden, who is reportedly eyeing a run, has garnered greater support in early public opinion polls Sanders quickly picked up the support of the rest of Vermont’s congressional delegation. Rep. Peter Welch (D-Vt.) issued a statement Tuesday morning endorsing Sanders, and Sen. Patrick Leahy (D-Vt.) followed suit several hours later.“We have to win, and I think Bernie’s in a position to do that,” Welch told, noting that his colleague had “been through the crucible” of a presidential campaign. “He has experience and he’s got a solid message and the tools to deliver it. So I think Bernie can do real well.”Though Welch supported Sanders’ 2016 campaign, Leahy backed former secretary of state — and eventual nominee — Hillary Clinton.“We have a strong field of candidates, and Bernie’s entry makes the field even stronger,” Leahy said Tuesday afternoon in a written statement. “Bernie and I had a great talk today. I’m proud to support my fellow Vermonter, a proven leader with a strong message.”Though Sanders devoted much of his announcement to his own campaign platform, he wrote scathingly of the Republican incumbent he hopes to take on in the November 2020 general election."You know as well as I do that we are living in a pivotal and dangerous moment in American history," Sanders wrote. "We are running against a president who is a pathological liar, a fraud, a racist, a sexist, a xenophobe and someone who is undermining American democracy as he leads us in an authoritarian direction.""I'm running for president," he continued, "because, now more than ever, we need leadership that brings us together — not divides us up."Trump responded Tuesday afternoon by saying that Sanders had “missed his time.”“I like Bernie because he is one person that, you know, on trade he sort of would agree [with me] on trade,” the president continued, speaking in the Oval Office. “The problem is he doesn’t know what to do about it.”Locally, Vermont Republican Party chair Deb Billado called on Sanders to resign from Congress, noting that he missed many Senate votes when he ran in 2016.“Vermonters deserve a full time senator,” she said in a written statement. “If Senator Sanders is keen on continuing his presidential campaign [then] he must resign and vacate his seat immediately.”A former mayor of Burlington who was first elected to Congress in 1990 and won reelection to the Senate last November , Sanders mounted an unexpectedly strong presidential campaign four years ago. He nearly tied Clinton in the Iowa caucuses and handily defeated her in the first-in-the-nation New Hampshire primary election . In total, the senator won 23 primaries and caucuses, roughly 13 million votes and 46 percent of the pledged delegates to the Democratic National Convention."Together, you and I and our 2016 campaign began the political revolution," Sanders wrote Tuesday in his email to supporters. "Now, it is time to complete that revolution and implement the vision that we fought for."Though Sanders is hardly the first candidate to enter the race, he brings to it several key advantages: high name recognition, a massive email list and a built-in donor base. In Tuesday's announcement, he pledged to run "an unprecedented and historic grassroots campaign that will begin with at least a million people from across the country."Sanders flexed his fundraising muscles immediately Tuesday morning. Within 3.5 hours of joining the race, his campaign said that he’d raised more than $1 million.A self-described democratic socialist, Sanders has distinguished himself in Congress as an avowed opponent of economic inequality and as the leading champion of single-payer health care and free college tuition. But unlike the 2016 Democratic primary, in which he was the sole progressive alternative to Clinton, the 2020 race features several prominent liberals.Four fellow senators seeking the party's nomination — Cory Booker (D-N.J.), Kirsten Gillibrand (D-N.Y.), Kamala Harris (D-Calif.) and Elizabeth Warren (D-Mass.) — cosponsored Sanders' signature Medicare-for-all legislation after the 2016 election, as did Sen. Jeff Merkley (D-Ore.), another potential candidate. Merkley and U.S. Rep. Tulsi Gabbard (D-Hawaii), who joined the race last month, were among the few members of Congress who endorsed Sanders in 2016. But many political observers view Warren, a fellow New England progressive with a passion for public policy, as the greatest threat to Sanders' candidacy.The Progressive Change Campaign Committee, a liberal advocacy group, endorsed Warren last month — well before Sanders announced his intentions.“We believe that Elizabeth Warren is the most electable Democrat and would be the best president for America,” PCCC cofounder Adam Green toldTuesday. “I think it’s also true that Bernie Sanders running ultimately helps Elizabeth Warren by creating a gravitational pull toward her core issues.”Though some have argued that Sanders and Warren could split the progressive vote and hand the nomination to a moderate Democrat, Green argued that “they’re both better off having the other in the race” because neither would be “seen as out on a limb by themselves.”Democracy for America, which was founded by former Vermont governor Howard Dean after the 2004 election, sought to recruit Warren to the 2016 race but later endorsed Sanders. Executive director Charles Chamberlain on Tuesday called Sanders a “fantastic leader” who “has built a strong, broad-based section of grassroots support across the country.”He said that DFA would likely make an endorsement later this year or early next year — and that, for now, each candidate would have to court its members.“I think Sanders is likely to put in a strong showing, but he definitely doesn’t have our support locked up,” Chamberlain toldSanders is likely to face skepticism from those who believe that a septuagenarian white male should not lead the Democratic Party into the 2020 election — particularly when the field features many women and people of color. But in his interview with VPR, Sanders argued that Democratic voters should take a meritocratic approach to picking their nominee."We have got to look at candidates, you know, not by the color of their skin, not by their sexual orientation or their gender and not by their age," Sanders said. "I mean, I think we have got to try to move us toward a nondiscriminatory society which looks at people based on their abilities, based on what they stand for."Sanders’s 2016 campaign was criticized for being insufficiently diverse and failing to connect with voters of color — a point his former campaign manager, Jeff Weaver, conceded last month in an interview with the New York Times . “Was it too male? Yes. Was it too white? Yes,” said Weaver, who is not expected to reprise his role as manager in 2020. “Would this be a priority to remedy on any future campaign? Definitely, and we share deeply in the urgency for all of us to make change."Alumnae of the 2016 campaign have also alleged that it failed to take seriously allegations of sexual harassment and discrimination. In his interview with CBS on Tuesday, Sanders said that, “in retrospect, some of the people that were hired should not have been hired, and some of the women went through experiences that they should not have.”He continued, “This has been an issue that has upset me, and we're gonna rectify it in this campaign.”Weaver indicated last month that he would not reprise his role as campaign manager, instead serving as a senior adviser. The Daily Beast reported Tuesday that Sanders had tapped Faiz Shakir, political director of the American Civil Liberties Union, to manage his campaign.Though Sanders enters the race in a stronger position than he did in 2016, he continued to characterize himself as he has throughout his career — as an underdog."They may have the money and power," he wrote. "We have the people."