The Taoiseach has ruled out any possibility of coalition with Sinn Féin. The Fianna Fáil line is that such a move would be in contravention of Article 15 of the Constitution, which states that "the right to maintain military or armed forces is vested solely in the Oireachtas."
It follows, or so the argument goes, that as long as Sinn Féin is judged to have any links with the IRA, it cannot be a party to government, although its TDs may sit in the Dáil and on Oireachtas committees, including those concerned with the security of the state.
Leave aside for the moment that Fianna Fáil's own entry into the Dáil was effected on pretty dubious constitutional grounds. Its present line is opportunist and hypocritical. Unionists aren't the only people who wonder why it is a good thing for Martin McGuinness and Bairbre de Brún to hold important ministries in the Stormont executive, but that a totally different set of rules apply, not for the first time, "down here".
On Monday night's Questions & Answers, Brian Cowen explained - at least as I understood him - that the executive in the North was especially devised for the political purpose of conflict resolution and that, anyway, it is under the jurisdiction of the British government. He seemed to imply that if London was prepared to tolerate Sinn Féin's links with the IRA and allow them into government, so be it.
This State, however, is a republic with a constitution whose rules must be observed.
Clever, but there is another argument. Those who voted for the Belfast Agreement in this State (over 90 per cent of the electorate) did so in the belief that the Irish Government was an equal partner with the British in devising the settlement. That is why the referendum was held in both parts of the island.
The Taoiseach has repeatedly stressed, quite rightly, that the most important success of the Belfast Agreement was that it enabled the elected representatives of parties with links to paramilitary groups to come in from the political wilderness and play a part in the running of the state.
It's probably pedantic to labour this point. We all know that, as far as Bertie Ahern is concerned, there is always more than one way to skin a cat. If Sinn Féin emerges from this election with more seats than, say, the Progressive Democrats, the constitutional difficulties in the way of any deal will seem suddenly much less important.
WE will begin to hear more about recognising the will of the people as expressed through the ballot box, the importance of strengthening the peace process and accepting the commitment of Gerry Adams and his colleagues to democratic politics. There will probably be another act of decommissioning to underline all this.
Privately, Fianna Fáil TDs will begin to tell sympathetic journalists that many of the party's traditional supporters are sick to death of the PDs and Mary Harney's posturing on the high moral ground. Whatever about Sinn Féin, the party hasn't put up posters saying that Fianna Fáil isn't to be trusted and it wasn't Gerry Adams who compared the most popular Taoiseach ever to Ceaucescu.
What's more, they may well add, peace in the North remains Bertie's most significant political achievement. He recognises the contribution that Adams and those close to him made. But the Belfast Agreement is looking a bit tattered just now - the FARC adventure and other signs of IRA restiveness, the marching season, renewed violence in North Belfast, and so on. Perhaps it's time to do something for Sinn Féin?
Forgive me if I sound cynical. I don't mean to. But it is hard to take Fianna Fáil's current line on no deal with Sinn Féin entirely seriously. It may be, as some commentators have suggested, that Gerry Adams and those close to him are not interested in participation in government.
Yet. The party is playing a long game which involves building a strong base in both parts of Ireland.
BUT Sinn Féin needs to do well in this election. The appointments of Martin McGuinness and Bairbre de Brún to the Stormont executive were important in steadying the foot-soldiers of the Republican movement in Belfast and Derry. Now Adams has to show that the Republican movement can continue to make progress towards its traditional objectives by political means.
Coalition is probably not on the cards at the moment, but there are good practical reasons why Bertie Ahern might want to do a deal with Sinn Féin for its support in the new Dáil. For a start, it would be preferable to coping with a posse of greedy and unreliable independents. There are elements of Sinn Féin's manifesto, particularly in regard to the North, which would be quite acceptable to Fianna Fáil. It's hard to see Bertie objecting to the proposal for a Minister of State to oversee the full implementation of the Good Friday agreement.
It was interesting, watching Questions & Answers on Monday night, just how determined Brian Cowen was to reassure CaoimhghíÓ Caoláin that money would be available to save essential medical services in Monaghan. It looked to me like these were two politicians who understood each other very well.