Hillary Clinton has seen a sharp drop in polls in the past two weeks, and while many pundits assume it’s just Donald Trump enjoying a post-nomination bump, there could be another more troubling reason — a mass exodus of Bernie Sanders supporters driven away by what many see as unfair attacks.

Clinton had hoped to be sailing to the nomination at this point, with a nearly insurmountable lead over Bernie Sanders and likely a pair of big wins ahead in New Jersey and California to end the primary season. It was supposed to be a time of bringing her party together, but instead, the tension between Clinton’s camp (and the Democratic Party leadership) and Sanders supporters is rising.

That was on display earlier this month at the Nevada State Democratic Party Convention, where supporters of Bernie Sanders complained that their votes were ignored in a process tilted to Clinton’s delegates. That led to sharp rebukes both from the Democratic National Committee and the Nevada state party, both of which called out Sanders supporters for their alleged violence (though there were no reports of violence at the conference itself).

As Salon writer Conor Lynch noted, it only widened the divide between Clinton and Sanders supporters.

“Meanwhile, the Clinton camp and the Democratic establishment have seemingly decided that their best bet at unifying the party is to take the despicable actions of a few individuals (and by despicable I don’t mean booing Democratic leaders or being impolite, but making threats or using violence, even though the apparent ‘violence’ that erupted in Nevada recently was largely manufactured by the media) to generalize about an entire popular movement. “Establishment figures have accused Sanders supporters of having a ‘penchant for violence’ (ironically, a famous Clinton supporter was arrested for physically attacking a female Sanders supporter this week), and have even claimed that Sanders himself is inciting violence. Sanders has repeatedly condemned any and all violence, and has never — absolutely never — given the impression that violence is acceptable.”

This divide between Sanders supporters and Hillary Clinton isn’t just an imagined one. A series of polls have shown that Clinton is losing the support she once held among those more formally aligned with Sanders. Nate Cohn of the New York Times noted this troubling trend for Clinton, finding that her support among Sanders voters has dropped around 10 or 15 percentage points in recent weeks. More Sanders supporters now have an unfavorable view of Clinton as well, he wrote.

“Exactly what’s driving the shift is hard to say. What’s clear is that Mrs. Clinton’s challenge isn’t totally superficial. Just 20 percent of Mr. Sanders’s supporters have a favorable view of her in the most recent New York Times/CBS News survey, while 47 percent have an unfavorable one.”

And the Clinton camp may be pushing them further away still. This week, Bernie Sanders called on Clinton to debate him in California, keeping a promise she had made earlier in the campaign to hold a final debate in May. Clinton, likely seeing no political advantage, declined the invitation.

.@BernieSanders to @TheView: Clinton declined CA debate because she "doesn't want to go face-to-face" on the issues https://t.co/m93g0ivaqw — ABC News Politics (@ABCPolitics) May 24, 2016

Sanders seized on her decision, saying she backed out of the deal that Clinton herself had sought when she wanted more debates early in the schedule to help her performance in New Hampshire.

“The state of California and the United States face some enormous crises. Democracy, and respect for the voters of California, would suggest that there should be a vigorous debate in which the voters may determine whose ideas they support,” he said in a statement released by his campaign. “I hope Secretary Clinton reconsiders her unfortunate decision to back away from her commitment to debate.”

Hillary Clinton still has time to bring in Sanders supporters — and likely will earn higher support once she wraps up the nomination — but she will have big trouble in November if she keeps pushing them away with her unforced errors.

[Photo by Alan Wong/Getty Images]