Different rules apply to byelections. They can be a bit of a lottery, with voters giving governments mid-term kicks or giving a chance to a celebrity or anti-establishment party.
For a 30-year period in Irish politics, no Government party succeeded in winning a seat in a byelection. The Labour Party broke that pattern in October 2011 when Patrick Nulty won the seat in Dublin West left vacant by the death of Fianna Fáil's only TD in Dublin, Brian Lenihan.
Now Mr Nulty himself, who later severed his connection with the Labour Party, is vacating the seat after admitting sending inappropriate messages to a 17-year-old girl on Facebook. It is an unusual situation having a second byelection in the same constituency in the one Dáil term. While the first byelection happened within a year of the Coalition coming to power – and before it had lost its sheen – it still provides something of a form guide for how this byelection will go.
Within minutes of Mr Nulty’s resignation, Fianna Fáil’s David McGuinness was installed as the favourite. He came second in the byelection in 2011 against all the odds – garnering an impressive 21.7 per cent of the vote.
Socialist Party candidate Ruth Coppinger was not far behind, on 21.1 per cent of the vote. Indeed, both candidates were tied after the fourth count with Mr McGuinness surviving the count on the basis of having a higher percentage of first-preference votes.
The constituency, taking in most of Dublin 15, is split almost evenly between middle-class and working-class areas. Fine Gael's candidate in the byelection, veteran councillor Eithne Loftus, made little impression. There has been talk that Fine Gael will parachute in a big celebrity to stand here – the likes of Senator Eamon Coghlan or Kenneth Egan – however, the likeliest candidate could be Kieran Dennison, who stood in the general election in 2011.
There won't be a huge queue forming to become the Labour Party candidate, given that Mr Nulty stood for the party in 2011. Allied to that is that support for the party has fallen significantly. The chances of the party winning a seat is remote. Two local councillors, Mary McCamley or John Walsh, seem the most likely. Sinn Féin has not developed the same profile or presence in this constituency as it has elsewhere in Dublin, but things don't stand still. Paul Donnelly got 9 per cent of the vote in 2011 and will probably get a greater share this time, but not enough to be in with a shout.
It is going to boil down to the big two. There is little doubt Mr McGuinness will top the poll, but will he stay sufficiently ahead of Ms Coppinger to take the seat?