The arrest of Gerry Adams has exposed the deep division between Martin McGuinness and Peter Robinson. They are supposed to function effectively as joint First Ministers, defusing tension on the street and delivering a consensus approach to challenging situations.
That has sometimes happened in the past, but by now they are unable to show a common front on any issue that could divide their followers.
Yesterday Mr McGuinness, clearly furious, developed a complicated conspiracy theory explaining the arrest as an attempt to damage Sinn Fein in the elections.
The real damage is in the longer run. Mr Adams is one of Sinn Fein's biggest vote-getters. Yet the accusations which swirl around him make it unlikely that another party will ever enter a coalition with Sinn Fein in Dublin while he is its leader.
"We have seen that dark side (of policing) flex its muscles in the course of the last couple of days," Mr McGuinness (below) added ominously. These figures were somehow in league with, or being manipulated by, "people who were hostile to the peace process and who have very publicly associated with newspaper articles in which they were pledged to destroy Gerry Adams' political career".
He means disillusioned IRA veterans who gave taped interviews to the Boston College archive on condition that they would not be released during their lifetimes. He also seemed to be referring to writers like Ed Moloney and Anthony McIntyre, who organised the Boston project.
Yet Mr Moloney and Mr McIntyre fought a bitter legal battle to keep the tapes out of the hands of the PSNI. Both may be questioned themselves if they show up in Northern Ireland.
There was no conspiracy to release the material, only a police investigation taking its course in a plodding and predictable way.
Once the existence of the tapes and their allegations was known, the PSNI had no choice but to try to obtain them. Failing to do so would open them to sanctions from the Police Ombudsman, or legal action from any of the 10 people left orphaned when Jean McConville was abducted, shot in the back of the head and buried on a beach.
This was an atrocious, high-profile crime and the police could not legally ignore any evidence. In the absence of an agreed way to deal with Troubles-era crimes, investigations will inevitably be piecemeal, a case of catch-as-catch-can for the police.
Raymond White, a former head of CID, who retired from the PSNI with the rank of Assistant Chief Constable, knows the procedures.
The allegation, so far as we know, is that Mr Adams was an IRA commander at the time of Mrs McConville's death. He has always denied this.
Mr White said: "When people suggest that someone directed them to commit an offence, you must see precisely what information you have to put to the alleged leader.
"Legally, detectives should not consider politics. They follow where the evidence takes them, seeing what corroboration is available and what further investigations are indicated."
This means interviewing the people who may have information and weighing up what they have to contribute. In this case, several other people have been arrested and questioned before Mr Adams.
The timing was partly in Mr Adams' gift. He agreed to meet the police in Antrim on Tuesday. He could have remained in the Republic and asked for a later date.
"If you have the material there and you have no other fresh lines of inquiry, why would you delay in arresting someone? Adams is no different than any other suspect," Mr White said.
"Are you going to delay it because someone is on holiday, or getting married, or expecting a child? The system does not work that way."
Mr McGuinness doesn't see it that way, because it is a colleague and friend who has been arrested and because he sees a political impact on Sinn Fein.
Mr Robinson (right) is all for the police. "I would suggest to you that it would be political policing if the PSNI did not question those deemed to be involved in any way," he said, urging Sinn Fein to give up others who might be involved.
That was not the approach he took when his councillor, Ruth Patterson, was arrested, admittedly on a much lesser charge of sending a grossly offensive electronic communication.
Then, the DUP rallied around Ms Patterson and denounced her treatment. In the end she apologised and the charges were withdrawn, but not before a storm of protest from the DUP.
For devolution to be secure we need to reach a place where politicians can weather such scandals. It is normal in most democratic parties that a politician accused of a serious criminal offence is suspended until the investigation was concluded. Instead, Sinn Fein has closed ranks, as the DUP closed ranks when its member was arrested.
We need a better approach than this. We need an approach where political leaders will give leadership to the whole community – not just defend their own faction and friends.
Stormont won't collapse as a direct result of this, but the devolution settlement is being weakened by the fallout.
Every moment of stress becomes a crisis as, like a sickly patient, the administration lurches from one close call to the next.
It is in very bad shape to handle the marching season and any difficulties that may bring.