A nasty dispute erupted into public Wednesday over the leadership of Wellstone Action, the nonprofit created to honor the memory of Paul Wellstone, the late senator and a lion of the DFL.

The organization is removing the senator’s surviving sons David and Mark Wellstone from the board, causing an uproar among some of Wellstone’s most steadfast supporters.

The conflict threatens to divide some of the most important fundraisers and operatives in the DFL heading into an election year that many in the party view as the most consequential in years. The Associated Press first reported the board’s move to boot the Wellstone brothers.

Sam Kaplan, an influential DFL attorney and ambassador to Morocco under President Barack Obama, is representing the Wellstone sons and two other former board members. He told the Star Tribune that the dispute originated when the board refused to investigate basic financial questions raised by the board treasurer.

“It’s really shameful,” Kaplan said in an interview Wednesday. He was joined by Rick Kahn, a founding board member with close ties to the Wellstone family, who was removed from the board in November.

Wellstone Action is highly regarded in progressive circles for training candidates, operatives and volunteers, including U.S. Rep. Tim Walz, now a DFL candidate for governor.

The board said in a statement that the dispute arose from a difference of opinion about the direction of the organization.

It singled out Kahn, the Wellstone siblings and former board member Ron DeHarpporte for actions that “indicate that they don’t support the long-term vision of the organization.”

Removing the Wellstones “is not a decision we took lightly, but it was the necessary resolution,” the board said.

In a separate statement, co-founder Jeff Blodgett said that the actions of “certain former and current board members” had created “an untenable tension” over the organization’s “ongoing emphasis on expanding inclusivity and equity.”

Blodgett was Obama’s campaign manager in Minnesota, while Kaplan served as a major fundraiser.

Both men were personally close to Wellstone. Blodgett called the removal of Mark and David Wellstone “personally and professionally difficult for many on the board, including myself.”

Kahn, the longtime treasurer, said he noticed an increase in spending of $200,000 over budget last summer, as well as a sharp decline in cash balance.

“This was unprecedented in the history of the organization,” Kahn said. “I raised these questions, and properly so, as my legal obligations as treasurer of the organization are to ask questions about financial matters.”

Kahn sought a financial audit, which the board resisted, he said. Even after completing the audit, the board refused to share it with Kahn, the Wellstone sons and Kaplan.

Instead, Kahn said he and DeHarpporte, who shared the same concerns about the financial questions, were removed from the board.

Kahn, who grew close to the late senator first as a student at Carleton College where Wellstone was a professor, said he is not making allegations of impropriety, but wants his questions answered.

In response to some of the questions Kahn raised, Blodgett released an additional statement and shared a copy of a forensic audit. Calling the concerns “red herrings,” Blodgett said that “not only did the forensic audit find that there were no issues, but it found that Wellstone Action ended the year with a balanced budget.”

Blodgett said that the Wellstone brothers, Kahn and DeHarpporte were offered a copy of the report and underlying records subject to “a reasonable confidentiality agreement.”

He also refuted the assertion that Kahn and DeHarpporte were removed because of the financial questions they had raised. Instead, Blodgett said, their roles were not renewed “because it had become clear that they no longer supported the mission of the organization.”

The document that Blodgett shared was a Feb. 2 letter from Eide Bailly, a Minneapolis accounting firm. The letter detailed the steps it took to examine Wellstone Action expenditures. “We found no evidence of any improper payments based on our examination of the supporting documentation,” it concluded.

Paul Wellstone, his wife, Sheila, and their daughter Marcia were among eight people killed in a plane crash in northern Minnesota on Oct. 25, 2002, just weeks before he was to face voters for re-election. The DFL fared poorly in that election, including the loss of Wellstone’s seat, and Kahn gained a measure of notoriety for a fiery speech at Wellstone’s memorial service that was later criticized as overly political.

An effort to settle the Wellstone Action dispute fell through this week, Kaplan said, leading to the removal of the Wellstone sons.

Kaplan said he is astounded by the turn of events: “They will have kicked off the board David and Mark Wellstone, Ron DeHarpporte and Rick Kahn — four of the people who are by definition the closest people in the world to Paul Wellstone and his legacy.”