More than 50 liberal groups signed a letter Monday to presumptive Democratic presidential nominee Joe Biden criticizing his response to the emerging protest movement against police brutality, warning that failing to embrace a more aggressive agenda risks alienating the African American voters he needs to win the election.

The letter pointed to Biden’s recent promise to add $300 million for community policing programs, a plan that activists say would undermine their efforts to push for systemic changes, such as defunding police forces.

“It is a slap in the face to black folks,” said LaTosha Brown, the head of Black Voters Matter, an Atlanta-based civil rights group that signed on to the letter. “We’re in the middle of the largest uprising and protests against policing and unfair and unjust policing, and the biggest supporters to your campaign have been black people, and you come out and say you’re going to reward the police? What message does that send?”

The letter, which Brown said was first organized by several black-led groups, warned Biden that he needs to move more forcefully to remedy what they see as the ugly legacy of policies he pushed, such as the 1994 crime bill he helped write that put more police on the streets and, critics say, fueled mass incarceration of African Americans.

“As the presumptive Democratic nominee for President, you have a moral responsibility in this moment,” the groups wrote in the letter, which was first reported by the New York Times. “Making amends for the harm you’ve caused is an important first step, but it is no longer enough.”

The wide coalition of groups that signed the letter signals the challenges Biden faces in balancing his need to energize his party’s liberal base, newly galvanized by the wave of protests following the killing of George Floyd, while maintaining his appeal to moderate voters and grappling with his pro-police past.

Biden has so far distanced himself from some of the more dramatic ideas being pushed by activists, saying last week that he does not support defunding police departments. But while he secured the nomination largely because of strong support from black voters, the liberal groups criticizing him are warning that he could lose that edge if he does not meet the moment on police reform.

“You cannot win the election without the enthusiastic support of Black voters, and how you act in this moment of crisis will play a big role in determining how Black voters — and all voters concerned with racial justice — respond to your candidacy,” the groups wrote.

Biden’s campaign did not respond to requests to comment on the letter.

The former vice president gave a brief address days after Floyd’s killing in Minneapolis police custody, backing a ban on the kinds of chokeholds that led to Floyd’s death and promising to unveil a more robust policy in coming weeks.

He detailed his plan to increase funding in an op-ed published last week in USA Today, writing that a better response than defunding is to “give police departments the resources they need to implement meaningful reforms, and to condition other federal dollars on completing those reforms.”

“I’ve long been a firm believer in the power of community policing — getting cops out of their cruisers and building relationships with the people and the communities they are there to serve and protect,” he wrote. He added: “Every single police department should have the money it needs to institute real reforms like adopting a national use of force standard, buying body cameras and recruiting more diverse police officers.”

The NAACP supported Biden’s pushes as a senator to increase funding for community policing in the mid-2000s.

Today, many liberals say Biden’s views are out of date.

“The conversation has really evolved around police brutality,” said Varshini Prakash, the co-founder of the Sunrise Movement, a liberal climate change group that also signed on to the letter. “We have moved on from tweaks to the police systems. It’s not just building more goodwill between police and communities.”

Prakash said her group signed the letter because she sees a pattern: The same groups are hurt most by climate change and police brutality.

“It’s the same story again and again of who gets hurt and who survives and thrives in the midst of crisis,” Prakash said. “If you want the support of black and brown people, if you want the support of young people, this is an issue that we really care about.”

In the letter, the groups demand that Biden push ideas that were laid out in an agenda by the Movement for Black Lives, including supporting reparations for black people. Biden has said he wants to study that issue.

The group also called on him to defund police and prisons and move the funds to paying for health care, housing and education. Biden’s campaign should support calls for ending funding for any police, including training, equipment and overtime, according to the letter.

On the $300 million for community policing, the groups said, “That is not the answer,” arguing that the federal push for community policing has directly led to the deaths of black Americans because the funds have been used for training programs that instruct officers on “threat neutralization techniques” that have been fatal at times.