David Trimble insists that, under the terms of the Belfast Agreement, Gerry Adams cannot sit at the new Stormont cabinet table unless the IRA has started to hand over weapons. Gerry Adams argues that the decommissioning clauses of the Agreement should not be applied unilaterally to the IRA, but must somehow also be brought to bear on the guns held by the British army and the RUC.
Not for the first time, the issue of decommissioning threatens to put the entire peace process into reverse. The Spanish government's ultra-cautious response to Wednesday's ceasefire declaration by ETA, the Basque separatist organisation, threatens to snag any Basque peace process on the same thorny question.
However, handing over weapons is not a necessary and essential aspect of conflict resolution, as the Spanish themselves know perfectly well. In the early 1980s, a significant sector of ETA did a deal with the Spanish government in which its prisoners were released, and its exiles returned, without surrendering a single bullet. None of the hundreds of activists involved has returned to violence. Some of its political representatives now sit comfortably at the heart of the Spanish, and Basque, establishments.
In 1968 ETA launched an armed campaign against Gen Franco's security forces in pursuit of an independent Basque Country. When ETA killed the dictator's prime minister, Admiral Carrero Blanco, in 1973 many Spanish democrats secretly applauded. But the organisation revealed a less heroic face the following year, when a bomb in a Madrid cafe killed 12 people.
The death of Franco in 1975 was followed by a surprisingly fast and relatively bloodless transition to democracy, in itself a kind of peace process. This transition was based on the principles of national reconciliation and consensus. The parties which had fought the traumatic 1936-39 Civil War agreed not to reopen old wounds.
Both Republicans and Francoists had carried out appalling atrocities during the Civil War, and the Francoists continued to use terror as a matter of policy for the duration of the dictatorship. In a remarkable climate of mutual generosity, parties with a great deal of each other's blood on their hands sat down at the same table. They hammered out a democratic constitution acceptable to all the major players except, crucially, Basque nationalists. Even the moderate Basque Nationalist Party advocated abstention during the constitutional referendum of 1978, though they subsequently accepted, with some ambiguity, the institutions it created.
Meanwhile, the advent of democracy had split the radical Basques who supported ETA's "armed struggle" into a "military" wing (ETA-M) and a "political-military" grouping (ETA-PM). ETA-M's commitment to terrorism remained unqualified until last week's ceasefire. ETA-PM, however, took advantage of a number of amnesties to create a political party, EIA, largely led by high-profile former ETA prisoners. This party operated more or less independently of ETA-PM, and participated, as a dissident voice, in the elaboration of the constitution.
Meanwhile, ETAPM took on the role of "guarantor" of what the new party considered acceptable. To put it more bluntly, if the government did not meet EIA's minimum conditions for participation in democratic politics, ETA-PM would (and did) kill people. In time, the party became seriously embarrassed by its military wing's unbridled enthusiasm for this task.
Both ETAs had responded to democracy with an escalation of increasingly indiscriminate terrorist attacks, with an aggregate of 110 fatalities in 1980 as against 16 in 1975. For a period, ETA-PM was actually the more feared group, attacking even tourists. In 1979, seven people died and many more were injured in three virtually simultaneous airport and train station explosions. ETA-PM also targeted members of the government party.
However, EIA was simultaneously beginning to advocate the total cessation of "armed struggle". After a bitter internal debate, the most significant ETAPM leaders agreed that EIA should negotiate a resolution of the conflict with the government.
Mr Mario Onaindia, a veteran ETA leader condemned to death, and subsequently reprieved, in the notorious 1970 Burgos trial, suddenly found himself having dinner with the interior minister. They agreed that ETA-PM's prisoners, exiles, and activists would be "socially reinserted". Though many of them were guilty of, or suspected of, very serious crimes, no charges would be pressed against them.
"Nobody ever suggested they should give up their weapons," Mr Onaindia told The Irish Times last June. (He has since suffered a serious heart attack and could not be contacted again for this article). "The project was one of reconciliation, and those who gave up armed struggle were taken at their word." Nor were they required to express any regret for their past actions, nor to give any information about comrades who rejected the deal and continued their "war".
What happened to the arms they controlled? "I think they may have decided, on their own account, to render them useless," said Mr Onaindia. "But they did not have to do so."
Mr Onaindia is now a senator for the Spanish Socialist Party. He has reappraised radical nationalism in terms which Conor Cruise O'Brien might recognise. But, unlike Dr O'Brien, he supports the Northern Irish peace process.
He believes decommissioning was never important in Spain for three reasons. Firstly, the Spanish transition to democracy implied that no-one came to the table with clean hands - everyone bore some responsibility for past atrocities. This is something that unionists do not generally seem to recognise.
Secondly, there had been no really spectacular, Eksund-type, arms seizures in the Basque Country. These, he says, have created a real fear of enormous arsenals of IRA heavy weaponry in Northern Ireland. (A point bitterly underlined, since our conversation, by the Omagh bombing). ETA-PM simply did not have such stockpiles, he told me. (Those who suffered in the Madrid bombings of 1979 might be surprised to learn this).
Thirdly, the IRA's ongoing "policing" role within its own community depends on armed back-up, which makes people sceptical about their willingness to let their guns rust away. ETA-PM did not play such a role to any significant extent.
Mr Onaindia has outspokenly opposed ETA-M's continuing terrorist campaign over the last 15 years. But, he told me last June, he remains in favour of "social reinsertion" for its members, on the sole condition of a sincere commitment to democratic politics. Even for today's ETA, which regards his views with implacable enmity? "If they agreed to accept democracy, why not?"