“I have traveled across the country meeting with dozens of Cory Booker supporters, and it is clear to me that the donor community is strictly adhering to Senator Booker’s publicly articulated wishes that he does not welcome independent support (a position he re-articulated just this month),” Phillips said.

Phillips did not indicate in the statement that he would switch to aiding a different Democratic candidate such as former Gov. Deval Patrick of Massachusetts, who recently entered the race and said he would accept help from a super PAC in order to “catch up” in pursuit of the nomination.

“I remain firm in my belief that Senator Booker is uniquely qualified to unite and heal Americans across this country at this critical point in our history, and I still believe that he has a path to victory in Iowa and in the Democratic nomination contest,” Phillips said. “Respecting the Senator’s wishes, Dream United will cease operations effective immediately.”

Dream United was no longer the only outside group supporting Booker: A new super PAC formed by the candidate’s supporters in New Jersey in November, called United We Win, plans to spend $1 million trying to help Booker break out of the crowded Democratic field.