D.C. Mayor Muriel E. Bowser and two other key parties involved in the beleaguered merger of Pepco and Chicago-based Exelon said Tuesday that they can no longer support the plan, all but dooming a deal that would have created the nation’s largest electric utility.

Bowser’s team had negotiated for the utility companies to pay the District $78 million dollars in exchange for D.C.’s support for the $6.8 billion merger, which already had approval from New Jersey, Delaware, Maryland and federal regulators.

The mayor’s plan would have cushioned rate increases for D.C. residents for four years, but it was rejected last week by District regulators who said it was “not in the public interest” and would exacerbate an existing imbalance in which federal taxpayers and businesses subsidize residential rates in D.C.