Sen. Bernie Sanders (I-VT) responded to a letter on Thursday, which accused some of his supporters of making “hateful, violent and racist threats” toward people associated with the Working Families Party, which endorsed his rival Sen. Elizabeth Warren (D-MA).

Black leaders – including Black Lives Matter leaders, like co-founder Patrisse Cullors – signed a letter, which condemned the “hateful, violent, and racist threats” from people who identify as Sanders supporters. A draft of the letter, obtained by Splinter News, claimed that Sanders supporters have called black leaders “Uncle Tom,” “Slave,” and “Cunt.” The alleged threats followed Sanders’ loss of the WFP endorsement, according to the letter.

The letter, via Splinter, reads in part:

The WFP made a decision, with its members and supporters and staff, and there is now conflict over the substance of that decision. But let’s also be clear — the WFP is under new leadership. For the first time in its history, Maurice Mitchell, a Black man with decades of experience building movements and strengthening our democracy, alongside Nelini Stamp, a working class, woman of color and a gifted organizer with a long list of accomplishments, are now at the helm of the Party, where they should be. And apparently, some folks aren’t happy about it. These incredible leaders who led an organization to take a risk by lifting up the leadership of Black, Latinx, Asian and Pacific Islander and white communities in coalescing around a candidate with enough time to engage their communities deeply ahead of the 2020 election, are being threatened on a daily basis, by self-identified Sanders supporters, with hateful, violent and racist threats. “Uncle Tom.” “Slave.” “Cunt.” These kinds of threats have no place in our movements, and are reminiscent of the threats Black people would receive when daring to vote even though the white supremacists would try and discourage Black people from doing so. The virulent, racist attacks on these leaders are unacceptable and dangerous. What do we do when racism and sexism is present in progressive movements? What is the prospect of strengthening democracy when old habits just won’t die? Many of us, the undersigned, are no stranger to these kinds of attacks—too many of us receive threats like these ones every day because we dare to organize our people towards freedom. But if we hope to take back this democracy, if we dare to struggle for electoral justice, if we really want a world where Black lives do in fact matter, all of us must take a stand against these real and persistent threats. … We refuse to concede to white terror from the Left as well as the Right. We can argue about the differences between Sanders and Warren, but not if we can’t be distinguished from our real opposition.

The leaders continued, demanding the Sanders campaign “unequivocally denounce the racism in its ranks, and issue a public statement separating themselves from these abhorrent attacks.” They also urged Democrats across the board – both Sanders supporters and Warren supporters – to come together to “defeat one of the most serious threats to peace and justice in our lifetimes.”

“We cannot wait to make justice real amongst the resisters — our lives literally depend on each other,” the leaders added in the letter.

In a tweet on Thursday afternoon, Sanders seemingly responded to the letter’s call for swift condemnation.

“This campaign condemns racist bullying and harassment of any kind, in any space,” Sanders tweeted. “We are building a multiracial movement for justice — that’s how we win the White House”:

This campaign condemns racist bullying and harassment of any kind, in any space. We are building a multiracial movement for justice — that’s how we win the White House. — Bernie Sanders (@BernieSanders) September 19, 2019

National co-chair for the Sanders campaign, Nina Turner, also condemned the alleged threats outlined in the letter.

“Anyone directing racist, sexist &otherwise personally derogatory tweets/messages towards @MauriceWFP or anyone on his team @WorkingFamilies is a coward and is not in alignment w/ @BernieSanders or our collective mission,” she wrote:

Anyone directing racist, sexist &otherwise personally derogatory tweets/messages towards @MauriceWFP or anyone on his team @WorkingFamilies is a coward and is not in alignment w/ @BernieSanders or our collective mission. — Nina Turner (@ninaturner) September 19, 2019

The Sanders campaign signaled concern after losing the WFP endorsement to Warren, shaking up campaign staff in both New Hampshire and Iowa.

“Senator Warren strikes fear into the hearts of the robber barons who rigged the system, and offers hope to millions of working people who have been shut out of our democracy and economy,” WFP’s National Party Director Maurice Mitchell said of the Massachusetts senator following the coveted endorsement.