It is still early in the primary season. This weekend’s strong victory for Joe Biden in South Carolina, followed by the decisions of both Pete Buttigieg and Amy Klobuchar to suspend their campaigns, makes clear that the contest is very much undecided.

At the same time, Bernie Sanders clearly has assumed front-runner status. It is no surprise that this has his supporters jubilant, and has his opponents concerned and even frightened.

There surely are some Democratic donors and operatives who absolutely hate the thought of a Sanders nomination — whether for ideological or tactical reasons — and will do anything they can to prevent this. Such an attitude is foolish, because if Sanders continues to dominate the primary, this might suggest that he is the most “electable” of the Democrats.

The primary contest must play out in a way that is both fair and sufficiently “civil” that it is possible for all contestants to acknowledge the legitimacy of the process, and to rally behind the eventual winner.

At the same time, if Sanders is to claim the mantle of Democratic party leadership — which is different than leadership of the Vermont Liberty Union Party or Democratic Socialists of America — then he needs to start demonstrating a broader style of leadership.

He has recently shown signs of doing this, in his magnanimous speech after winning the Nevada caucus, and in an interview this past weekend, in which he praised both Joe Biden and Barack Obama, declaring that “we will come together” to support whoever is the Democratic nominee.

But the overall tenor of the Sanders campaign continues to be not simply adversarial, but antagonistic.

The three most powerful refrains by which Sanders contrasts himself to his Democratic competitors are these (I paraphrase):

1) “The Republican establishment is afraid, and wants to stop us. The Democratic establishment is afraid, and wants to stop us. They should be afraid. But they can’t stop us.”

2) “Unlike my competitors, I don’t take money from billionaires, I oppose billionaires, and stand for the 99% against the 1%.”

3) “The Democratic nominee should be determined by ‘the will of the people,’ and not the party elites and superdelegates.”

These rhetorical frames represent Sanders and his campaign as locked in a struggle with three enemies: (1) Billionaires and their paid political agents, which seem to include virtually all of his Democratic competitors (with the possible exception of Warren) and most Democratic politicians (except presumably those who have endorsed his campaign); (2) The Republican party establishment but also the Democratic party establishment whose leadership he now claims, both of which are (equally?) corrupt; and (3) Democratic establishment “superdelegates” whose representative claims are suspect because they were not selected through primaries.

Is it any wonder that many Democrats, and especially most Democratic elected office-holders, are averse to Sanders when he speaks and mobilizes in this way?

This presents real challenges.

Sanders’s left populist/social democratic message is the most powerful, compelling, and praiseworthy aspect of his campaign. It would be absurd to imagine that he could simply stop employing the rhetoric of class conflict between “the billionaire class” and “working people” — though it is not absurd to imagine that he could employ a wider range of rhetorical tropes, something his own recent appeals to “working families and the middle class” seems to concede. It is also absurd to imagine that he should stop highlighting the fact that his campaign is a grass-roots effort, fueled by volunteer activists and by small donors.

At the same time, it is not absurd to imagine that he might stop referring to virtually every one of his competitors as a veritable lackey of “the one percent.” For while such rhetoric might fuel Sanders’s base, it is also alienating to all of the other candidates and their bases, which represent large segments of the Democratic party.

Deploying such rhetoric is no way to promote party leadership or the kind of political unity that will be necessary to defeat Trump in November.

Equally troubling is the derisive way that Sanders talks about the party “establishment” whose nomination he seeks.

The Democratic Party, like all parties — even the increasingly hollow and weak ones that seem now to dominate liberal democracies around the world — is a political coalition of constituent groups. It has an “establishment.” This “establishment” includes rich donors, but also incorporates many constituencies — civil rights, reproductive freedom, environmentalist, labor — that are no less “grass roots” than Sanders’ supporters. The notion that the Democratic party is governed by a nefarious “establishment” that stands against “the will of the people,” and that Sanders stands with “the people,” is both risible and demagogic.

Wikipedia furnishes a very useful list of the 775 individuals who are designated “superdelegates,” i.e., unpledged delegates, for the 2020 Democratic convention.

Who are these people? One third (226) consist of Democratic members of the House of Representatives. All of these individuals were elected democratically in general elections. Many of them indeed represent Congressional districts that are larger than the state of Vermont that elected Sanders to the Senate (population roughly 660,000, smaller than Nancy Pelosi’s Congressional District in San Francisco). A second group consists of the 48 Democratic members of the U.S. Senate. A third consists of the 28 Democratic governors, all elected chief executives of states. The other roughly 400 consists of elected members of the Democratic National Committee, including the chairs and vice-chairs of each state’s Democratic party. Almost every one of these people is a state or local elected official or party activist. Of this group, 14 are currently linked to the Biden campaign, 13 to the Sanders campaign, and almost all of the rest are both unpledged and undecided. Nina Turner is a “superdelegate.” So is Alexandria Ocasio-Cortez, Ilhan Omar, Rashida Tlaib, Ro Khanna, and Pramilya Jayapal — Sanders’s main Congressional supporters.

This group of “superdelegates” comprises 16% of the delegate total.

Because of 2018 Democratic rule changes that represented concessions to Sanders supporters, none of these people can vote in a first round of balloting.

As a result, it is impossible to see anything underhanded about the participation of superdelegates in subsequent deliberations and rounds of voting, if no candidate has obtained a majority on the first ballot. These are the new rules that Sanders and his supporters pressed for.

When no one candidate can command a clear majority, does it make sense to exclude the many party regulars from the process of determining the Presidential nominee of the party to which they have dedicated their working lives? Does it make sense to exclude the hundreds of Democrats who have themselves won general elections and who currently wield governing power in Congress and in the states and localities that comprise the U.S. political system?

Representative Pramila Jayapal of Washington state, a strong Sanders supporter who is co-chairwoman of the Congressional Progressive Caucus and herself a Sanders-committed “superdelegate,” was quoted in the New York Times: “If Bernie gets a plurality and nobody else is even close and the superdelegates weigh in and say, ‘We know better than the voters,’ I think that will be a big problem.”

She is right.

But it will be an equally big problem if Sanders shows up at the Convention and says to the thousands of Democratic activists assembled there: “I won 40% of the pledged delegates through the obscure and often open primary rules of the fifty states, and the rest of you are all corporate lackeys and I beat you and you should thus hand me the nomination and rally beneath my ‘democratic socialist’ flag.”

I oppose the demonizing of Sanders and his campaign. The activism that Sanders has promoted for the past five years represents a major contribution to the party and to American politics more generally. Furthermore, I believe that Robert Reich might well be right, and that Sanders may turn out to be “the safest choice.”

But Sanders also might not be the safest choice for the Democrats.

In any case, Sanders is no longer a maverick Independent working from the margins of normal politics to expand the boundaries of ideological debate. He is now a leading candidate seeking the Democratic Party’s nomination to run for President of the United States.

If he wants to lead the Democrats into the 2020 elections, to win the presidency and to power victories in the House and the Senate, then he needs to start thinking and acting like a leader of the entire party, and as someone who is truly vying for the votes of a wide range of Democratic constituencies and some independent voters too.

If he wants to exercise real leadership of the party, he will need to persuade Democrats who are not now his supporters to become his supporters, even if he is their second choice or maybe even their third.

Sanders, like any genuinely radical politician, faces genuine obstacles.

But it is up to him to surmount these obstacles in a way that empowers the party he seeks to lead. This won’t be easy. But there is no alternative.

Jeffrey C. Issac is James H. Rudy Professor of Political Science at Indiana University, Bloomington.