A Vermont liberal and presidential candidate is drawing huge, largely-white crowds in liberal cities. He’s urging the Democrats to move left and break from the centrism that defined the Clinton era. And he’s shooting up in the polls, even though he entered the presidential race as a long-shot.

The rise of Bernie Sanders, at least right now, closely resembles that of Howard Dean 12 years ago. Dean, the governor of Vermont, held rallies in New York and Seattle in the summer of 2003 that drew more than 10,000, as Sanders did in Madison, Wisconsin on Wednesday. Dean was viewed as the man of principle by liberals back then, one of the only leading Democratic candidates to have opposed the Iraq War.

Now it's Sanders who is taking the bold, progressive stands the party’s left wants: opposing the Trans-Pacific Partnership, calling for a government-run, universal health care system and free tuition at state colleges and casting the U.S as a country where the wealthy have way too much power.

The icon of the left in 2003, Al Gore, endorsed Dean. Now, Elizabeth Warren, the liberal darling and Massachusetts senator, is praising Sanders and leaving open the possibility of backing him over Hillary Clinton.

Dean, in a traditional sense, lost in 2004, winning only the Vermont primary and being mocked for an overly enthusiastic speech dubbed the “Dean Scream.” But his influence helped push the eventual nominee, John Kerry, who had initially voted for the Iraq War, towards a more anti-war stance in the general election against George W. Bush. And Dean’s pioneering use of the Internet to both raise money and organize supporters was an early model for President Obama’s operation in 2008.

The rise of Sanders, who polls show has sliced Clinton's lead in in both Iowa and New Hampshire to fewer than 20 points, in part reflects a long-existing divide between the Democrats’ more liberal wing and its establishment one. Jesse Jackson’s presidential campaigns in 1984 and 1988 melded strong African-American support with enthusiastic backing from some white liberals, but he was not able to win the nomination, in part because of opposition from the Democratic establishment. (Sanders, then the mayor of Burlington, backed Jackson's 1988 run, helping Jackson win the Vermont caucuses.)

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“Jesse Jackson is a serious candidate for the presidency. He was always serious; it was just the political scientists and the other politicians who belittled his campaign, trivialized his efforts, and disdained his prospects,” the liberal magazine “The Nation” wrote in a 1988 editorial, using language that mirrors how Sanders and his supporters are currently complaining about how the press is covering his candidacy.

Like Jackson, Bill Bradley in his 2000 challenge to then-Vice President Gore, Dean in 2004 and President Obama in 2008 all drew support from deeply-liberal activists who did not embrace the party establishment candidate. Dean and Obama in particular were known for drawing huge crowds, even in states where they did not win.

On the eve of the 2008 Democratic primary in Pennsylvania, more than 35,000 people came to hear Obama speak in Philadelphia. Hillary Clinton won the state a few days later by almost 10 points.

Obama, particularly in the early stages of 2007, showed some signs of being the next Howard Dean, a path that would not led him to victory. But he was able to build deeper support than Dean in the establishment of the Democratic Party. Obama was well-liked enough by party elites that many in the party opted either to endorse him or remain on the sidelines instead of backing Hillary Clinton, the early front-runner.

So after Obama won Iowa, he was able to get the support of major figures in the party like Ted Kennedy and Kerry.

The win in Iowa was pivotal for Obama, and he did that in part by changing the electorate there by getting more college students and independents to vote than in previous caucuses. The Iowa victory established Obama as a true contender, and he was able to combine winning states with a strong liberal tradition (like Wisconsin) with states with huge black populations, like Mississippi, to defeat Clinton.

But Obama only narrowly defeated Clinton, who won a number of states because of her strength with moderate and conservative Democrats, a huge bloc in the party. In Pennsylvania, in 2008, for example, Clinton won was favored by 17 points over Obama among self-described moderate Democrats, who were 40 percent of the primary electorate there.

So Sanders likely needs to win Iowa and then develop a base broader than white liberals to win the primary. The latter may be the bigger challenge. Iowa is full of the kind of white liberals that like Sanders. But his surge so far is concentrated among white Democrats and liberals, while polls show black and Hispanics overwhelmingly and more moderate Democrats favor Clinton.

A liberal insurgent candidate without strong black support or appeal to moderates will struggle to win in states like South Carolina and Pennsylvania.

The lack of party’s establishment could also be a problem for Sanders. The majority of Democratic senators have endorsed Clinton. She raised more than $45 million in the first three months of her campaign, compared to $15 million by Sanders. Even Dean has endorsed Clinton.

These endorsements are intended to send a subtle message to Democratic voters: Clinton can win the general election, Sanders cannot. If Democratic voters are convinced Sanders will lose to the GOP nominee, it will be hard to him to win the primary.

Both Sanders and Clinton seem aware of these dynamics. The Vermont senator’s advisers are already talking about him taking steps to increase his support among black and Hispanic voters. Clinton, meanwhile, has taken a number of stands in line with liberal activists, such as declaring any immigration reform bill must include a pathway to citizenship for undocumented immigrants.

What’s unclear is how if Sanders can grow his base. During the 2008 primaries, as Obama gained strength, lawmakers like Rep. John Lewis of Georgia withdrew their endorsements from Clinton to back Obama. Obama was able to not only win white liberals but blacks in overwhelming numbers.

What Sanders has to hope for is that the nature of the Democratic primary has changed since the days of Dean and Jackson. The Democratic Party, in the Obama-era, has become more liberal on many issues and the influence of the left is strong. Could black Democrats overwhelmingly back a white candidate like Sanders? Could there be more Democrats who consider themselves liberal in 2016 than in past primaries? Could a populist candidate like Sanders get conservative and liberal Democrats behind one person?

The Obama wave of 2008 caught many Democrats by surprise. No candidate had melded white liberals and black Democrats so successfully. Sanders too will have to create some kind of new coalition to win.