Joseph R. Biden Jr.’s campaign effectively dropped its longstanding opposition to receiving the assistance of super PACs on Thursday, opening the door for wealthy supporters to spend unlimited amounts of money to try and lift him in the Democratic primary.
The move represents a stark reversal and an implicit acknowledgment of his weakened position in the contest. He entered October with only $9 million in the bank, a fraction of his leading rivals.
Mr. Biden had explicitly denounced support from a super PAC in his 2020 run and had previously said he would not have blessed one if he had run in 2016. As recently as a month ago, when a possible pro-Biden super PAC surfaced, his campaign denounced the effort.
But on Thursday, Kate Bedingfield, his deputy campaign manager, softened that stance, blaming the barrage of ads and attacks from President Trump and his allies and accusing them of interfering in the Democratic primary.
“Let’s be clear: Donald Trump has decided that the general election has already begun,” Ms. Bedingfield said. “He and his allies are already spending massive amounts of money on paid television and digital advertising to intervene directly in Democratic primaries with the goal of preventing Joe Biden, the opponent that Trump fears most, from becoming the Democratic nominee.”
She said Mr. Biden maintained his desire to remove private money from federal campaigns but “nothing changes unless we defeat Donald Trump.”
Faiz Shakir, the campaign manager for Senator Bernie Sanders, immediately criticized the flip.
“The former vice president has been unable to generate grass roots support, and now his campaign is endorsing an effort to buy the primary through a super PAC that can rake in unlimited cash from billionaires and corporations,” Mr. Shakir said.
During a town hall-style event in Marshalltown, Iowa, on Thursday evening, Mr. Sanders laced into Mr. Biden further. “Well, Joe Biden didn’t have to convince me not to start a super PAC,” he said, in response to a question from an audience member about Mr. Biden telling Mr. Sanders during his 2016 campaign run that he didn’t need to start a super PAC.
Mr. Sanders later added: “I don’t need a super PAC. I am not going to be controlled by a handful of wealthy people. I will be controlled by the working people of this country.”
Mr. Biden himself had framed his opposition to super PACs around the ability to appeal to middle-class Americans. “I’ve said it before and I’ll say it again. To speak to the middle class, we need to reject the super PAC system,” he wrote on Twitter in April.
The Biden campaign had maintained its anti-super PAC posture in late September even as Mr. Trump’s attacks were underway, citing it as a matter of principle.
“The attacks aimed at this campaign from dark money groups helping Donald Trump spread his outlandish lies and slander have only served as a reminder of the urgent need for campaign finance reform,” T.J. Ducklo, a Biden spokesman, said then. “Which is exactly why since the beginning of this campaign, Biden for President has not and will not welcome the help of super PACs.”
While the Biden campaign statement on Thursday did not explicitly embrace a super PAC, Tiffany Muller, the president of End Citizens United, which opposes big money in politics, said that Biden campaign staff confirmed that Mr. Biden was dropping his opposition to a super PAC.
“It is incredibly disappointing to see Vice President Biden completely reverse his position now that times are tough,” Ms. Muller said. “I don’t think we could say it as well as he did when he said, ‘People can’t possibly trust you’ if you accept support from a super PAC.’”
Officials involved in the pro-Biden super PAC discussions a month ago had included Larry Rasky, a former aide to Mr. Biden, Mark Riddle, a political strategist, and Philip Munger, a prominent Democratic donor.
“We intend to fight back against the lies and distortions we’re seeing now from Trump, his allies, the Russians, and the Republican Party,” Mr. Rasky said. “While other candidates have groups supporting their efforts, no other Democrat has to fight this two-front war. We know Joe Biden is the best candidate to defeat Donald Trump — and so does Donald Trump.”
The Democrats planning the pro-Biden super PAC, which include Julianna Smoot, a former top fund-raiser for Barack Obama, have also contacted Steve Schale, a Florida-based strategist, about playing a key role, according to party officials familiar with the conversations.
Jonathan Martin, Alexander Burns and Sydney Ember contributed reporting.