After a defeat in the Nevada primary, Bernie Sanders faces mounting challenges in reaching Party stalwarts and expanding the electorate. Photograph by Jim Young / Reuters

What Bernie Sanders is trying to accomplish is ludicrous. His age (seventy-four), political label (socialist), disposition (grumpy), and aesthetic (rumpled) make him the most improbable Presidential candidate of 2016 not named Trump. At the start of the race, the gap between Sanders and Hillary Clinton when it came to name recognition, élite Party support, polling, and fund-raising was nearly as wide as it could possibly be between two candidates vying for the nomination. Sanders has been maddeningly vague about how he would pass what would be the most ambitious and expensive Democratic agenda in modern history. When he’s forced to talk about foreign policy he seems hesitant and uncertain. Nearly every answer involves some reference to his opposition to the 2003 Iraq War.

And yet his campaign against Hillary Clinton has defied all expectations. Iowa was essentially a tie, and in New Hampshire he defeated her by twenty-two points. Saturday in Nevada, he kept the race close, losing by just five points in a state where he started behind by fifty-four points in the state’s first poll last year. While raw vote totals have not been reported for Iowa and Nevada, which hold caucuses, it’s certain that if the first three states were combined, Sanders has won many more votes than Clinton has so far in 2016.

Sanders has also already fared better than two recent Democratic insurgencies: Bill Bradley’s 2000 campaign against Al Gore and Howard Dean’s campaign against half a dozen Washington insiders, in 2004. But there’s been only one successful Democratic insurgency in recent decades—Barack Obama’s, in 2008—and Sanders is not on the same trajectory. There were two major components to Obama’s success. First, Obama expanded the Democratic electorate. This started in Iowa, where turnout hit a record in 2008 when Obama attracted young voters, independents, and even Republicans to caucus for him. If the traditional Iowa electorate of a small number of older Democratic partisans had shown up, Clinton would have defeated Obama. After Obama won Iowa, he opened a crucial second front against Clinton when he began to win over non-white voters. Even after building that strong coalition, he barely defeated Clinton; depending on how you count, she ended up winning more over-all votes than Obama.

Sanders has been expanding the electorate, but not by enough, and the over-all turnout numbers in 2016 are not meeting or exceeding the Obama milestones. Sanders is dominant with young people and political independents—according to the latest figures, he won voters between the ages of eighteen and twenty-nine by eighty-two to fourteen in Nevada—but it’s not enough to make up for his deficits among other groups. The Nevada results show Sanders is having trouble breaking into traditional Democratic constituencies, like African-Americans and older voters, especially among women. Clinton won African-Americans by seventy-six per cent to twenty-two per cent in Nevada. Voters over forty-five years old made up sixty-three per cent of the Nevada electorate, and Clinton won that group by more than two to one.

There was one bright spot for Sanders in the Nevada results. He appears to have cut into Clinton’s support among Hispanics. As with other groups, it was younger Hispanics who came out for him. The more well known Sanders is among younger voters of all races and backgrounds, the better Sanders performs. His problem is that, as the total number of primaries held accelerates over the next few weeks, he might not have enough time for voters to get to know him, and, even given his impressive fund-raising, he might not have the resources to truly compete in dozens of states.

Nevada is a quirky state—it has a transient, overwhelmingly urban population—and the outcome there shouldn’t be over-interpreted. Sanders could still pose a challenge to Clinton for many weeks to come. Insurgencies usually fail, but they often tell us something about the shape of politics in the near future. Clinton may defeat Sanders’s millennial army in the primaries, but to succeed she and other Democrats will need its support for years to come.