A new Pew poll released today finds that supporters of Bernie Sanders are split on whether they think the Democratic Party will unite behind Hillary Clinton if she’s the nominee, with nearly half saying that the party “will have disagreements that keep many from supporting Clinton”:

Meanwhile, last night, Sanders suggested to Rachel Maddow that his campaign might try to peel super-delegates away from Clinton, even if he trails narrowly in both pledged delegates and in the popular vote at the end of the Democratic nominating contests. While this is mostly about keeping his supporters energized (and sending money), it’s possible it portends at least a bit of turbulence.

All of which raises a question: How hard will it be to unite the party behind Clinton, if she does win the nomination, as currently looks likely?

Democrats I spoke to about this today identified a key dynamic: they expect a number of prominent Democratic elected officials and activists to play a high profile unifying role, by arguing that the party needs to unite against the horror of a President Trump or President Cruz. That’s an obvious argument to make, but the Democrats who might step into this role — and how they might go about doing this — are worth watching in the weeks to come.

First and foremost among these Dems: Elizabeth Warren. The Massachusetts Senator has remained carefully neutral in the Dem nominating contest, but her recent praise of Sanders was widely seen as highly newsworthy. “‘He has put the right issues on the table both for the Democratic Party and for the country in general so I’m still cheering Bernie on,” Warren said.

This actually positions her well to play unifier later. Warren, who is seen as an authoritative voice of economic progressivism by rank and file Dems, can argue that Sanders played an important role in forcing her (and his) issues — inequality, stagnating wages, Wall Street accountability — into the public dialogue and pulled Clinton to the left on them. (Clinton’s Wall Street plan draws on some elements of Warren’s agenda.) Now that this important mission has been accomplished, she might argue, it’s best to unify against the GOP candidate who would roll back Wall Street oversight and opposes any minimum wage hike while pressuring Clinton to remain as good on their issues as possible.

Another Dem to watch is Hawaii Rep. Tulsi Gabbard, who recently cut a heart-felt ad for Sanders. Gabbard won a lot of credibility among rank-and-file Bernie backers when she quit as vice-chair of the Democratic National Committee amid a battle over the ideal number of Dem debates. Two other high-profile Sanders supporters to keep an eye on are Dem Reps. Raul Grijalva and Ellison, the co-chairs of the Congressional Progressive Caucus. Warren, Gabbard, Grijalva and Keith Ellison are super-delegates, so they’ll be uniquely positioned to shed some light on the inner workings of the process — and possibly vouch for its integrity — if there are tensions around it.

If figures like this call for party unity and a recognition that Clinton has won among pledged delegates and voters, it could carry some weight. It’s worth noting that Ellison, for his part, has already pledged to campaign for Clinton if she’s the nominee.

Still other figures worth watching are activists who are well outside the Democratic establishment. There’s Larry Cohen, the former head of the Communication Workers of America, who has become an enthusiastic backer of Sanders — and who, as a well regarded progressive, could help illustrate the stakes for workers in the coming general election. Or there’s climate activist Bill McKibben. He has enthusiastically championed the transformative potential of a Sanders presidency and has talked about how the fate of the planet may depend on the next inhabitant of the Oval Office.

If Clinton wins the nomination, figures such as McKibben might then turn towards noting that, even if Sanders is more ambitious than Clinton is on climate, there is also an extremely stark difference between Clinton and any of the GOP presidential candidates: She would protect Obama’s Clean Power Plan and would keep the U.S. engaged in the global climate deal, and a GOP president would do everything possible to undermine both.

As Jonathan Chait notes, recent bad climate news only underscores the urgency of this deep, fundamental difference, and shows that it goes well beyond the question of whether to acknowledge climate science. The success or failure of real, concrete solutions that are currently being implemented is now what’s at stake. So the voices of climate activists more generally could help amplify the calls for unity, from the perspective of their particular issue.

It’ll also be interesting to keep an eye on some of Clinton’s more progressive supporters, such as senators Sherrod Brown and Al Franken. Both are well regarded among progressives, and Brown in particular has a lot of credibility on economic and trade issues and the challenges facing working people. They might be voices of outreach to Sanders supporters.

And then there’s also Barack Obama. He has left little doubt that he sees Clinton as his preference for securing his legacy. But he has also been very careful to praise Sanders for speaking to the discontent among rank-and-file voters over the forces that have blocked or slowed progressive change during the Obama era. While Sanders’s campaign has often seemed premised on implicit criticism of that slow pace of change, Obama might try to take on a high profile role in re-engaging younger voters by spelling out the dangers of a GOP presidency to their futures.

As Alex Seitz-Wald reports, some Democrats think that Sanders is trying to amass as many delegates as possible with an eye towards exerting leverage at the convention. If so, you could see the Clinton campaign making some concessions to Sanders on issues as part of her summer and fall campaign agenda — and figures such as Warren pointing out that this shows Sanders influenced Clinton in a positive way in advance of the general.