The botched Renewable Heat Incentive (RHI) was driven by Arlene Foster's desire to "curry favour with the rural electorate", according to a former DUP MLA.
David McIlveen broke ranks to heavily criticise the first minister's handling of a botched green energy scheme.
The one-time North Antrim MLA, who lost his seat in last May's election, said his party leader had "seriously misjudged the public anger" over an initiative that has left the Stormont administration facing a £490 million overspend.
He branded the scandal an "omnishambles" and claimed an internal storm was brewing within the ranks of the party about Mrs Foster's leadership.
Mr McIlveen described his former Stormont colleague as an "electoral liability" and expressed doubt she would be leader in the long term.
"Whilst the view in public is that 'Arlene's team' are as loyal and happy as ever, the reality in private is something very different," he said.
Writing in the News Letter, he added: "Does a party obsessed with winning elections want to move forward with a leader who appears incapable of facing up to their mistakes, and attacks on a personal level their critics even if they are members of their own party?
"I think the answer to that question is fairly obvious and therefore believe it is highly unlikely that 2020 Westminster elections will be fought under the existing DUP leadership."
Mr McIlveen suggested one reason Ms Foster designed the RHI in the manner in which she did was to appease voters outside Belfast.
"... the RHI scandal was most likely driven by more by a mixture of ineptitude and a desire to curry favour with the rural electorate rather than by something more sinister," he said.
The former MLA was critical of how former enterprise minister Jonathan Bell was treated when he broke ranks before Christmas.
"In any other context, Jonathan Bell MLA would be called a whistleblower," he said.
"Upon witnessing the way in which he was treated by the leadership of the party, I do not see how any member of the public who sees something going wrong in the civil service would feel inspired to raise issues with a DUP run department, after witnessing how their own people are treated."
He claimed dissent was growing within the DUP.
"The theatrics of a temporary step aside are largely down to party politics and of course no DUP leader will want to be seen to act at the behest of Sinn Féin," he said.
"However the much more significant story will be the storm that is quietly brewing within the DUP itself which Mrs Foster will be powerless in the long term to do anything about."
But DUP veteran Sammy Wilson said Mr McIlveen was "totally wrong" and claimed resentment at losing his assembly seat in the last election had motivated his attack.
"I don't think that it is representative," he said. "I think you have got to remember David probably has some motivation here because he is still feeling sore after having lost the election."
