IOWA CITY, Iowa (AP) — It was hard to miss Cheri Pichone's excitement about Bernie Sanders' second presidential run. She showed up to a recent Iowa rally decked out in Sanders gear, complete with a figurine of the Vermont senator and progressive icon.

But underneath her exuberance, the 36-year-old was still mad about the last Democratic primary, when Sanders' bid for the presidency fell short to Hillary Clinton.

"They cheated," she said, directing much of her anger at the Democratic National Committee. The party establishment, she lamented, was "actively working against us."

Pichone voted for Green Party candidate Jill Stein in 2016 and said she may vote for a third party again if Sanders doesn't clinch the nomination.

She's emblematic of a persistent group of Sanders supporters who won't let go of the slights — real and perceived — from the last campaign. The frustration is notable now that Sanders is a 2020 front-runner, raking in $18.2 million in the first quarter, downplaying concerns about DNC bias and highlighting his success in bringing the party around on liberal policies it once resisted.

Some establishment-aligned Democrats worry the party could lose in 2020 if lingering concerns about the last primary aren't put to bed.

"It has the potential to escalate, and it has the potential to help re-elect Donald Trump," said Mo Elleithee, a former spokesman for Clinton and the DNC.

The acrimony stems from a fiercely fought campaign and a sense among Sanders loyalists that party leaders privately favored Clinton. DNC leaders at the time scheduled fewer debates than Republicans and sometimes slated them for nights with low television viewership. Often opaque delegate allocation rules also contributed to a belief among some Sanders supporters that the primary was essentially rigged.

According to data from the Pew Research Center, the tension took a toll. About 81% of people who consistently supported Sanders during the primary season and were confirmed to have voted in the general election said they ultimately voted for Clinton, while 11% said they supported Stein or Libertarian nominee Gary Johnson, and 3% supported Trump.

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In a closely contested election, those moves away from Clinton may have factored into the results.

Since the election, party leaders have sought to smooth things over with Sanders and his supporters. DNC Chairman Tom Perez is planning a robust debate schedule. The rules governing superdelegates — party insiders who overwhelmingly backed Clinton — have changed.

Sanders has publicly expressed confidence in the process this time around, but in terms that suggest he won't soon forget 2016.

"In 2016, I think I will not shock anybody to suggest that the DNC was not quite evenhanded," he said during a CNN town hall in February. "I think we have come a long way since then, and I fully expect to be treated quite as well as anybody else."

In an interview Friday, Sanders campaign manager Faiz Shakir echoed that optimism.

"If you're talking to anyone at the Democratic National Committee who's there now, I'm sure they will tell you that their relationship with the Bernie Sanders campaign is great and that we are operating in good faith and we are talking to each other on an almost daily basis," he said. "Anyone suggesting that there's any kind of friction there is living in the past. They are living with some grudges that they are holding onto from a bygone time."

Still, the campaign has made some moves that raise questions about whether resentments from 2016 will linger. Briahna Joy Gray, formerly a liberal journalist who voted for Stein, is Sanders' national press secretary. Nina Turner, who called the DNC "dictatorial and pompous" in 2017, is one of his national campaign chairs.

And some of Sanders' most loyal supporters in the crucial early voting states say they're not ready to fully move on.

Nicholas Shaw, a 39-year-old from Concord, New Hampshire, spent his recent birthday watching Sanders speak. Like Pichone, he said he wouldn't support the Democratic nominee if it's anyone other than Sanders.

"If they steal it from him again, I'll go independent or something other than that," he said. "The Democratic Party's on their last edge of me if they kind of try to screw him again."

Even in South Carolina, where Sanders lost momentum after a 47-point drubbing from Clinton, some supporters are still smarting over a process they believe was rigged.

"Lost might be a stretch," said Tom Amon, of Summerville, when asked how he felt about Sanders' ability to perform better in South Carolina than he did in the 2016 primary. "It was stolen from him."

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Woodall reported from Manchester, New Hampshire, and Kinnard reported from North Charleston, South Carolina. Associated Press writer Juana Summers in Davenport, Iowa, contributed to this report.

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This story has been corrected to reflect that Sanders' campaign manager is Faiz Shakir, not Fiaz Shakir.