His Donegal South West seat vacancy opened immediately after his election and if the opposition manage a repeat of weekend victories it would whittle away the Government’s Dáil majority.
Yesterday Taoiseach Brian Cowen said he had yet to consider when to hold the by-election. He had been pressed by Sinn Féin’s Caoimhghín O Caoláin to move it as quickly possible.
Sinn Féin would be expected to mount a serious challenge for the seat with Senator Pearse Doherty, who got within 1,200 votes of Mr Gallagher and Fine Gael’s Dinny McGinley in 2007.
In the three council electoral areas of the constituency Fianna Fáil lost seats.
But it would take the combined Sinn Féin and Fine Gael support to best Fianna Fáil’s last outing when Tánaiste Mary Coughlan topped the poll.
Labour is expected to run Frank McBrearty Jnr, the victim of Garda corruption, who surprisingly won a seat on the county council.
Fianna Fáil’s obvious, but not guaranteed, choice is Senator Brian O Domhnaill. His camp had a cool relationship with Mr Gallagher.
But it remains a constituency where Fianna Fáil would expect to win. Mr O Domhnaill said the Tánaiste’s popularity would help.
“Traditionally we had two seats and we [in Fianna Fáil] would expect to win a by-election if the proper strategy was adopted.
“It is a matter for the Government and Dáil when the by-election is held and for the party to decide who it puts forward.... but obviously I would be very interested to run,” he said.
Mr O Domhnaill would be a complicated choice because his brother, Seamus, was elected as an Independent councillor in defiance at Fianna Fáil’s failure to nominate him.
The senator said it was a mistake not to run a third candidate as his brother won a seat at the expense of Fianna Fáil’s sitting councillor.
Two vacancies have also to be filled in the Seanad, with elections expected in September. One vacancy is due to the death of Fianna Fáil’s Tony Kett, the other due to Labour’s Alan Kelly’s election as an MEP.
Fianna Fáil’s Seanad leader, Donie Cassidy, said because the seats will be decided by majorities in the Oireachtas, Fianna Fáil will win both.