Joe Biden’s campaign signaled to donors this week that Priorities USA would be its main big-money partner for the general election — a move that has alarmed some of Biden’s ardent backers, who fear the campaign has given outsize influence to a super PAC that many donors associate with the party’s loss in 2016.

Biden’s campaign on Wednesday called Priorities USA, which was founded in 2011 to support President Barack Obama’s reelection, “a leader” among the groups working to defeat President Trump and an “organization of proven effectiveness.” The statement was viewed as a sign to wealthy backers that they should give to Priorities over other groups.

But some prominent Biden supporters said the decision had alienated outside groups that had formed since 2016 and helped turn out voters for Democratic wins in subsequent elections. One of those groups is Unite the Country, which boosted Biden through the primaries.

Among top Democrats pushing the campaign to accept help from a broader constellation of groups is Rep. James E. Clyburn (D-S.C.), an influential figure whose endorsement was pivotal to Biden’s momentum toward the nomination.

“It’s a horrible mistake to put all the eggs in one basket,” Clyburn said in an interview with The Washington Post. “I believe very strongly that everybody has a role to play. No one person, no one entity can be all things to all people. It just can’t happen. One size does not fit all.”

Clyburn is a prominent advocate of Unite the Country, and his daughter is on the group’s board.

Jim Messina, campaign manager for Obama’s 2012 reelection run and an adviser to a different superPAC, American Bridge 21st Century, said the party’s donors need to invest in many independent groups to beat Trump.

“Democrats have one goal this election and that’s to defeat Donald Trump. We need a unified effort across multiple organizations focused on the same outcome,” Messina said. “One of the most important lessons Democrats learned in 2016 is we must invest in multiple efforts to win.”

On Thursday, Biden campaign spokesman Andrew Bates said there would be room for other groups, even as the campaign stood by its original statement: “We applaud Priorities for its work and leadership while fully appreciating the roles that other independent groups can and will play.”

At stake are hundreds of millions of dollars in independent spending for Biden by super PACs and politically active nonprofits that can raise and spend unlimited sums to try to influence elections.

Democrats are scrambling to build an operation to compete with President Trump, who has been fundraising for his reelection since 2017.

But as they seek to put up a unified front, Democrats have been dogged by internal battles over how to avoid the mistakes of 2016, when they were caught off guard by Trump’s unorthodox campaign and ultimate victory over Democratic nominee Hillary Clinton.

Some of the donors concerned with this week’s announcement said that the party made a mistake in leaning so heavily on Priorities USA in 2016, because it put too much control in the hands of a small group of overly influential players.

Under federal regulations, campaigns are not allowed to coordinate with independent groups that accept unlimited contributions. But campaigns can legally make public statements that signal support for or opposition to certain efforts.

The Biden campaign’s approval of Priorities USA was first reported by the Wall Street Journal on Wednesday. In a statement to the Journal, the campaign said: “As Democrats across the country come together to achieve this goal, we are pleased that Priorities USA will be a leader of an unprecedented and united community of organizations focused on winning in November.”

That statement came as Priorities USA, which poured nearly $200 million into supporting Hillary Clinton in 2016, announced that it would work with a coalition of prominent spenders coming together for the general election, including American Bridge 21st Century, Color of Change PAC and the Latino Victory Fund. Over the past year, Priorities has been running ads and litigating voter access issues in key general-election states in support of the eventual Democratic nominee.

In a statement, Patrick McHugh, executive director of Priorities USA, pointed to the coalition — dubbed a Partnership Advisory Committee — as an example of how Priorities USA is collaborating with other groups.

“We are grateful for everyone doing the hard work of defeating Donald Trump and are proud to partner with over 90 Democratic and progressive organizations,” McHugh said.

Jennifer Granholm, a former Democratic governor of Michigan and chair of American Bridge, said in a statement that her group is looking forward to working with Priorities USA “but only as equal partners in the fight to elect Joe Biden.”

“Let there be no misimpression: American Bridge will continue to lead the ‘super PAC’ swing state effort to defeat Donald Trump,” Granholm said.

The Biden campaign’s decision alarmed several longtime donors, who noticed that the Partnership Advisory Council did not include Unite the Country.

“I won’t give a penny to Priorities and will discourage anybody” from doing so, said John Morgan, a prominent Orlando donor whose fundraiser early in the primaries brought in $1.7 million for the Biden campaign.

He said fellow longtime Biden donors had expressed concern to him about Biden’s top advisers’ judgment in giving their blessing to Priorities, which those donors believe miscalculated its spending strategy in 2016. “They cannot be trusted with our money — again,” Morgan said.

Another longtime Democratic donor, who spoke on the condition of anonymity to describe private discussions, said there was “an explosion” of “aggressive and tense” reactions among fellow Biden donors, who thought the campaign was repeating a failed strategy.

“My opinion was always that Biden would be crazy to pick one,” the donor said. “This is not 2016. We lost in 2016 with this command-and-control structure. There are many groups that sprung up since 2016 on our side.”

Independent groups had been jockeying behind the scenes to persuade the campaign to avoid announcing Priorities as its favored group, according to people familiar with the conversations who spoke on the condition of anonymity to discuss private conversations.

“Unite was just trucking along, and their lawyer got a call from the campaign lawyer saying we are going to do this Priorities thing and we don’t need you anymore,” said a person associated with Unite the Country. “Over a period of about 10 days, there was an effort to try to negotiate.”

Unite the Country and its supporters pushed back against this plan, and they subsequently announced a joint project with American Bridge, a group that also works with Priorities, to raise $175 million to support the campaign.

During this period, Clyburn, whose daughter Jennifer Clyburn Reed works for Unite the Country, also made a personal overture to Biden on behalf of her group, according to people familiar with the call.

“These are Joe Biden’s friends. People on that board have given and raised millions of dollars,” said the person associated with Unite the Country. “Priorities is an entity that has existed for many years, and their allegiance is not to Joe Biden.”

“We respect a lot of the work that groups are doing out there, and we think that there are a lot of organizations that play a different skill set and expertise,” said Steve Schale, executive director of Unite the Country. “It’s good to have a lot of voices. You win elections by addition, not subtraction.”

Rep. Clyburn is frequently in touch with Biden — they last spoke Sunday, wishing one another a Happy Easter, Clyburn said — and he has told Biden directly about his strong feelings about the merits of Unite the Country and told him that the group’s work was a chief factor in his becoming the putative nominee.

Clyburn said he considered the super PAC’s resources when he decided to endorse Biden, whose campaign at the time was financially strapped. Immediately after Clyburn made the endorsement public, the group helped amplify his endorsement, taping radio ads and robocalls that went out throughout South Carolina and in states voting several days later on Super Tuesday. “I did it all with Unite the Country,” he said. “I don’t know where Priorities USA was throughout all of this.”

Clyburn said his daughter’s role with the group did not influence his position. In a statement, Clyburn Reed said she joined the super PAC “because of their inclusive approach . . . early in the primary which helped deliver the nomination to Joe Biden and because I know an amplified approach like that will be critical to winning in November.”

Other donors were concerned by the addition of Bill Knapp, a longtime political consultant who joined the Priorities-led effort and was a business partner of Biden’s top campaign adviser, Anita Dunn.

Knapp will serve as a consultant for Priorities and will not take a cut of advertising spending, according to the group. The firm he and Dunn own, SKDKnickerbocker, does not have a business relationship with Priorities.

A Biden campaign official, who spoke on the condition of anonymity to discuss internal discussions, denied any conflict of interest, saying Dunn was not involved in Knapp’s joining Priorities and had not made decisions about the campaign’s choosing Priorities as a favored outside group.