Democratic Party power brokers are rallying around Hillary Clinton, calling for unity and a focus on defeating Donald Trump. Are Bernie Sanders supporters willing to do the same?

A Bloomberg article published Wednesday warns that “nearly half of Sanders supporters won’t support Clinton.” It cites a June 14 Bloomberg poll of likely general-election voters, reporting that “barely half of those who favored Sanders—55 percent—plan to vote for Clinton.” The story adds, “22 percent say they’ll vote for Trump, while 18 percent favor Libertarian Gary Johnson.” The report indicates widespread resistance to a Clinton presidency among Sanders supporters, a dynamic that could help the senator as he negotiates the terms of his surrender.

Sanders is technically still in the presidential race. But Clinton has claimed the title of Democratic presumptive nominee, and the senator has acknowledged he doesn’t expect to win. “It doesn’t appear that I’m going to be the nominee,” he said in a C-SPAN interview released on Wednesday. On Thursday evening, Sanders is planning to deliver a speech that will outline his next steps.  In recent days, Sanders has turned his attention away from contesting the nomination and toward an effort to shape the Democratic agenda and the future of the party. Whether he can achieve his aims may hinge on how badly Clinton wants to win the support of his voters.

The Bloomberg report is only one indicator of support, or a lack of it, for Clinton. A CNN poll released Tuesday shows that 74 percent of Sanders supporters would vote for Clinton in a choice between her and Trump in the general election. Yet support for Clinton dropped when other options besides Trump were included in the poll. When asked to choose between Clinton, Trump, the Libertarian Party candidate Gary Johnson, and the Green Party candidate Jill Stein, only 57 percent of Sanders supporters said they would back Clinton. Eight percent said they would vote for Trump; 13 percent picked Johnson; and 18 percent went for Stein.

The poll also found that 49 percent of Sanders supporters had an unfavorable opinion of Clinton, while 47 percent reported a favorable opinion. That suggests that even if many Sanders voters don’t love the idea of a Clinton presidency, some will grudgingly support her anyway, especially if it comes down to a choice between Clinton and Trump.

Clinton may not have won over Sanders voters yet, but high-profile Democrats are coalescing around their presumptive presidential nominee. President Obama, Vice President Joe Biden, and Massachusetts Senator Elizabeth Warren have all endorsed Clinton. She is also currently beating out Trump in national polling averages. In the RealClearPolitics average, Clinton has 45 percent to Trump’s 39.2 percent, while The Huffington Post’s general-election model shows Clinton at 44.3 percent to Trump’s 38.3 percent.

A lot can change between now and the general election. As Nora Kelly explained, “polls are snapshots, meant to capture voter sentiment at a particular moment.” People are not very good at predicting what they will do in the future: Once the presidential race officially becomes a contest between Clinton and Trump, many Sanders supporters may eventually come around to supporting the Democratic nominee.

What voters decide to do may also depend on how Sanders wraps up the race. Sanders has signaled a willingness to work with Clinton in the future, and made clear he wants to see Trump defeated. But Sanders has effectively pit himself against her as he works to shape the party agenda. “Where we are right now with Secretary Clinton is we are negotiating,” he said during the C-SPAN interview, noting: “we have had real differences of opinion.” If Sanders decides to endorse, and enthusiastically support her candidacy, or formally exit the race ahead of the convention, his actions could go a long way toward convincing his supporters to do the same.

Clinton cannot afford to take Sanders supporters for granted. Huge numbers of voters continue to view her candidacy unfavorably, although Trump is even more unpopular. The question now is what Clinton is willing to do to win over skeptics who have stood by Sanders, and whether Sanders will turn the support he has won into political gain.