Washington (CNN) In what should be Democrats' strongest moment since November, a series of emotional and racially charged clashes are forcing the party to once again confront the problem that has plagued it for a year: How to incorporate the supporters of Bernie Sanders.

The Vermont independent senator himself is winning battles over the direction of the Democratic Party. He has emerged as a messaging leader on health care, appeared on a "unity tour" with the party's new chairman and helped craft a populist economic agenda for the midterm elections. Many Democrats even concede the possibility that Sanders could enter the 2020 presidential race as the party's frontrunner if he chooses to run.

But even as Sanders and party leadership increasingly make ties on Capitol Hill, infighting with roots in the ideologically loaded and often deeply personal 2016 primary are threatening to blow up the détente.

This new series of emotional and racially tinged arguments could shatter a fragile peace, forged in opposition to President Donald Trump, and undermine Democratic efforts to claw back control from Republicans in Congress during next year's midterm election season.

"Unity requires give and take. But it seems that it's just take, take, take from the Berniecrats," said Nina Turner, the president of Our Revolution -- the political organization that emerged from Sanders' 2016 run for president -- using a term, "Berniecrats," that Sanders supporters like Turner apply to themselves.

Turner was appointed by Sanders to the DNC's "unity commission" in the wake of the 2016 contest. Her comments have led other members of the 21-person commission to grumble that Turner is more interested in sowing discord as a publicity and fundraising tool. But in an interview with CNN, she refused to back down.

"The Berniecrats are being labeled as always wrong -- 'they don't get it, they're too emotional, they don't want to win elections,'" Turner said. "This is a hurtful environment, and people are human and do have feelings. And so both sides are just duking it out."

The anger that has simmered in Sanders' camp since the 2016 Democratic National Convention bubbled to the surface in comments from some of the Vermont senator's most prominent political allies and surrogates, particularly in two recent clashes.

First, three key Sanders backers -- National Nurses Union executive director RoseAnn DeMoro, pro-Sanders journalist Nomiki Konst and "People for Bernie" co-founder Winnie Wong -- publicly dismissed Sen. Kamala Harris' prospects of winning over the party's progressive wing. The pointed quotes were picked up online when a Mic report , published after the California Democrat was feted by top party donors in the Hamptons, went viral in late July.

Sen. Kamala Harris (D-CA) questions witnesses from the Trump Administration in the Hart Senate Office Building on Capitol Hill in June.

Many Democrats saw the criticism of Harris as a needless and counterproductive jab at a rising star. But Sanders' backers -- who tend to be younger and whiter than the overall Democratic electorate -- were stung by suggestions that their distaste for Harris is fueled by race, like those from liberal MSNBC host Joy Reid, who tweeted : "So black Democrats must go begging young white leftists who were not numerous enough to nominate their preferred pick last time?"

"So odd, no, that these folks have (it) in for Kamala Harris and Cory Booker," tweeted Neera Tanden, the president of the Center for American Progress.

The intense backlash provoked an equally sharp response from Sanders' allies, including Turner and the three who had initially panned Harris -- DeMoro, Wong and Konst, none of whom are white men.

Fight comes to the DNC steps

The online brouhaha set the stage for an in-person clash July 25 -- the same day the Senate would vote on a motion to proceed to the Republican Obamacare repeal bill , a coincidence that would lead some party officials to question Our Revolution's tactics and motives -- just outside the Democratic National Committee headquarters in Washington.

Turner led a group of 60 activists to deliver a petition to the DNC. Our Revolution had told DNC officials of its plans three weeks earlier, Turner said.

When they arrived, DNC senior staffers greeted them on the steps with boxes of donuts and bottles of water.

The building's security team uses crowd control measures when large crowds come, a DNC spokeswoman said. It's not an unusual step, particularly for a party that was hacked in 2016 and with the political world on edge after the shooting at a congressional baseball practice.

DNC political director Amanda Brown Lierman spoke to the group on the building's steps, thanking them for their activism. But Turner -- who is a Sanders-appointed member of the DNC's "unity commission," a DNC member and a long-time Democrat -- was upset she wasn't allowed into the building.

"We understand the fire code. It's not our first time delivering petitions. We get it," Turner said. But, she added, the DNC could have invited her and five people delivering the petitions into the building to sit down and briefly chat.

"And then we could have walked out in five or 10 minutes, unified," Turner said. "They didn't even do that."

The incident took on increased importance after Turner lashed out at the DNC in an interview with BuzzFeed , which was published late Wednesday.

DeMoro, whose nurses' union provided crucial backing to Sanders' 2016 presidential campaign, spoke to Turner after the story's publication. "I told her that the problem here is that she's a movement leader. She's speaking truth to power," DeMoro said.

Accusations of a double standard

Sanders' allies view any effort to diminish Turner as one designed to undercut Sanders.

The primary reason: Sanders struggled with black and Latino voters in the 2016 Democratic primary. To win the nomination if he opts to run in 2020, Sanders will need to expand his base of support. In Turner, his allies see a powerful black female figure whose prominence showcases his broader appeal.

"They would like to classify everyone as a 'Bernie Bro' -- as a white guy, an angry white man," DeMoro said.

"What I think that (BuzzFeed) story indicates is Nina's effectiveness as a leader," DeMoro said. "She is a leader. And movement leaders are always under attack. Especially black movement leaders. So the narrative is to try and make them look unhinged, imbalanced -- it's to make anyone who speaks truth to power look unstable."

In both the backlash over Sanders allies' criticism of Harris and the DNC incident, Turner said she saw "the system" -- Democratic donors, Hillary Clinton-aligned operatives, in particular -- "really trying to continue trying to drive a wedge between progressive people of color and progressive whites."

Nina Turner is seen in this October 2014 photo. (AP Photo/Mark Duncan, File)

"They're using identity politics as a weapon," she said. By criticizing black Democrats such as Harris, Booker or former Massachusetts Gov. Deval Patrick, Sanders supporters are "labeled as a racist and a sexist. But they don't say the same thing when their side comes out and attacks somebody like me."

That failure to defend her against racist attacks stings, said Turner -- adding that she's personally been called "Bernie's Omarosa" and "Bernie's Aunt Jemima."

"To be called that and not have an outcry from the tone police, it's hypocrisy," Turner said.

That's the Berniecrat leaders' view.

Elsewhere in the Democratic Party, lawmakers and strategists are complaining that Sanders' allies are forcing the party to revisit its 2016 divides -- at precisely the wrong time.

"It is not good for the rebuilding that needs to happen within the party for Democrats to be attacking each other, and I think in particular the attacks on Kamala Harris are fruitless and unfair," said Brian Fallon, who was Hillary Clinton's national press secretary and is now a senior adviser at the Democratic super PAC Priorities USA.

"Sen. Sanders is showing tremendous leadership in moving the Democratic Party in a progressive direction on issues from college affordability to Medicare for all," Fallon said. "But some of his supporters are undercutting that good work by trying to fast-forward to a 2020 presidential primary. We have too much important work that needs to be done before we start attacking people just because they're considered rising stars in the party."

Others also said it appeared Sanders' allies were firing a 2020 starting gun too early -- a charge both sides have now leveled against each other.

"On balance and in the long run, the Bernie team's spat with Kamala Harris has actually been beneficial to her -- it has raised her profile as a real contender in 2020 (otherwise, why would the Bernie folks feel so threatened?) and rallied the vast majority of the party in her defense," a Democratic operative said in an email. "That's not a good sign or look for Bernie Sanders and his team."

A moment for Sanders to speak up?

The complaints from Sanders' supporters come at what has the potential to be Democrats' strongest moment since Clinton's 2016 election loss.

The party leads Republicans in generic congressional polls. Its base is energized in a way Democrats haven't seen in years headed into the 2018 midterm elections. And a breach between President Donald Trump and Senate Majority Leader Mitch McConnell is increasingly visible, with Trump attacking McConnell on Twitter.

"So why in the world would the progressive forces that want to resist Trump, that want to win up and down the ballot -- why in the hell would we be fighting with each other?" another Democratic strategist said.

"A lot of Democrats who really very much care about the same set of progressive issues that Bernie Sanders cares about are champing at the bit to say 'What the f---?' with Our Revolution."

That strategist said Sanders needs to weigh in. "These things are being done in his name. Where's his sense of responsibility for reining these things in?"

A representative for Sanders said the senator, who is in Vermont during the congressional recess, could not be reached for comment.

Several Democrats acknowledged that the party badly needs Sanders, whose supporters have remained loyal, within its fold -- and said they see the recent dust-ups as disconnected from the Vermont senator and out of step with his post-election actions.

Tanden described Sanders as "a hugely important force" in defending the Affordable Care Act from the GOP's repeal effort.

She called him a "strategic leader in the amendment process," said Sanders "rallied the troops," and pointed to his use of a key committee post to force Republicans to drop elements of their health care bill through the enforcement of the procedural "Byrd Rule."

"I see, in his actions, him recognizing that we are facing the most right-wing administration in history. He himself has done a lot to unify people," Tanden said.

Carolyn Fiddler, the political editor and senior communications adviser for the progressive blog Daily Kos, said Sanders' allies should "sort out their differences with Democrats and shift their focus back to the task at hand sooner rather than later."

The DNC, meanwhile, would prefer to avoid a direct confrontation with Sanders' supporters -- even as members of the party's "unity commission" complain that Sanders' own appointees to that commission sniped at Harris and, in Turner's case, unloaded on the DNC.

"The DNC is focused on winning elections. That is our goal," said the DNC's Lierman, who met Turner's group of activists outside the party headquarters.

"And as we look at key races in 2017 and beyond, it's going to take progressives working together to bring about real change for working families. That is what we did when we defeated the Republican health care bill and that's what we will continue to do in races up and down the ballot," Lierman said. "We hope that all progressive leaders will join us in this fight."