Campaigns are about candidates, but they’re also about parties. Bernie Sanders’s impressive victory over Hillary Clinton in the New Hampshire primary isn’t just a triumph for Sanders, although his personal achievement can’t be denied. He ran an impeccable twenty-first century, high-tech campaign with a message that resonated with the voters and allowed him, a 74-year-old self-described democratic socialist, to beat a presumptive nominee who was popular with the party’s voters and held a formidable advantage in fundraising and endorsements from elected officials. Yet Sanders won—primarily because the Democratic Party has changed dramatically in the last two decades, becoming a much more liberal party that is receptive to Sanders’s call for a political revolution.

Changes in the ideological orientation of the party’s base explain also why Hillary Clinton is struggling despite her political talents and many advantages. Clinton’s biggest problem is that she’s a figure from the past: Her political identity as a national figure emerged in the 1990s, during the presidency of her husband, when she led a failed effort at health-care reform. The advantage that Barack Obama had in 2008, and Bernie Sanders has now, is that they were relatively unknown to the broader public, so they could craft an identity that seemed fresher than Clinton’s and better-suited to the moment. 

Clinton still frames issues in centrist terms that suited the triangulating 1990s better than the more liberal party of Obama’s last year in office. In making her chief arguments based on electability, pragmatism, and the lack of realism in Sanders’s policies, Clinton only reminded voters of the frustrations of the era when Bill Clinton often tried to split the difference between his own party and the hard right of Newt Gingrich’s congressional Republicans. 

To be sure, Sanders is older than Clinton, and he’s been an elected official for a long time. But his brand of democratic socialism was marginal in the party until now, and he’s been able to time his ascension to the national stage to the moment when the party’s base is most receptive to it. Sanders is the person of the hour in large part because he waited for the hour to emerge. 

A new poll released today by the Pew Research Center helps define the shift in the party that has created the Sanders wave. Democrats—especially if they are white, millennial, and postgrad—are increasingly likely to call themselves liberals:

In 2015, more Democratic voters identified as liberals (42%) than as moderates (38%) or conservatives (17%), based on an average of Pew Research Center political surveys conducted last year. In 2008, when Barack Obama defeated Clinton for the party’s nomination, 41% of Democratic voters called themselves moderates, while just 33% said they were liberals and 23% said they were conservatives. And in 2000, moderate Democratic voters outnumbered liberals by 45% to 27%.

This same data, though, shows the weak spots that might hurt Sanders as the race moves to the South and West, where the Democratic base is not so predominantly white. In states like South Carolina and Nevada, Sanders will have to win over black and Hispanic voters, with whom he lags behind Clinton. The Pew data gives a clue as to why this might be so. The very voters Sanders needs to win over are the ones who have been slow to join the Democrats’ shift to the left:

By contrast, more black and Hispanic Democratic voters characterized their views as moderate than liberal in 2015, and the self-described political views of both groups have remained stable in recent years. Last year, 42% of black Democrats called themselves moderates, 29% said they were conservatives and 27% called themselves liberals. Among Hispanic Democrats, 39% described their political views as moderate, 35% as liberal and 24% as conservative.

It is true that younger blacks and Hispanics are also trending liberal, but for now, there are enough moderate and conservative older blacks and Hispanics to give Clinton some breathing room.  

Clinton could still, of course, win the nomination. Her institutional advantages in terms of having elected officials and party elders behind her remain formidable. But whatever Bernie Sanders’s fate as a presidential candidate after Tuesday’s triumph, his campaign is the harbinger of a deep change in the Democratic Party. In coming years, Democratic politicians will have to echo Sanders’s slashing critique of Wall Street and his call for a far more robust welfare state if they want to hold on to the rising generation in their party. The future belongs to Sanders’s brand of Democrat.