(CNN) - Massachusetts lawmakers have voted to approve a measure that would give Gov. Deval Patrick the power to appoint an interim replacement for the late Sen. Ted Kennedy until a new election can be held - but it's still too soon for the bill's backers to claim victory.
The measure, which Wednesday afternoon passed the Massachusetts House and Senate, would not go into effect for 90 days - a period that ends just a month before the scheduled special election for a permanent successor to complete the remainder of Kennedy's Senate term - unless two-thirds of the state House voted to bypass the delay and enact the measure immediately.
Democrats have fallen just short of that mark, with a final state House vote of 95-59.
Patrick also has the power to declare an emergency, which would allow the provision to go into effect right away. An immediate appointment would give Democrats a crucial 60th vote in the U.S. Senate as the chamber weighs President Obama's health care proposal.
But Republicans have threatened to file suit if the governor makes that emergency declaration, and it's unclear what course a court fight might take.
Two Kennedy family associates have told CNN that Paul Kirk, longtime senior aide to the late Sen. Ted Kennedy, is the family's favorite to fill his vacant Senate seat – and that the late senator's sons have relayed this view to Patrick. One source said the late senator's widow,Vicki Kennedy, was among the family members supporting a Kirk appointment.
Asked if Patrick is on board, a source said "it is 75 percent there."
–CNN's John King, Gloria Borger and Rebecca Sinderbrand contributed to this report