Why all this talk about the IRA? I thought they'd gone away, you know? There was a pretty widespread perception that IRA members became ex-IRA members in 2005, after the IRA announced an end to its armed campaign and said it would work by "purely political and democratic programmes through exclusively peaceful means". That was also the year it decommissioned all its weapons – although maybe not quite all.

Is there a problem? There is a big problem. In May, Gerard "Jock" Davison, a man with a formidable IRA pedigree, was shot dead in the Markets area of central Belfast. This month his fellow former IRA man, and former friend, Kevin McGuigan was shot dead in the Short Strand, not far from the Markets. The dogs in the street said it was revenge for Davison's killing, carried out by IRA members – current or ex – and others.

And did the IRA kill McGuigan? It depends whom you believe. PSNI Chief Constable George Hamilton has said IRA members were implicated, along with dissidents and criminals, in a new group called Action Against Drugs. Gerry Adams and Martin McGuinness of Sinn Féin have said the murder was carried out by "criminals", not by the IRA, because the IRA cleared the stage 10 years ago.

Who is correct? Adams, McGuinness and Sinn Féin are on their own in their assessment. Unionists accept the word of the chief constable. "Why would we believe Gerry Adams when he was 'never in the IRA'?" was a comment heard regularly during the week.

So the IRA is back in action? It's much more nuanced and complicated than that. Hamilton was careful in his assessment of the state of the IRA. He said that although IRA members were involved in McGuigan's murder, their actions were not sanctioned by the IRA leadership.

There's an IRA leadership? Careful now. Hamilton would not use the term "army council". He said an IRA "hierarchy . . . enabled the leadership to move the organisation forward within the peace process". He also said the IRA "does not exist for paramilitary purposes", that a primary focus of the organisation was "promoting a peaceful, political republican agenda" and that the IRA was "committed to following a political path and is no longer engaged in terrorism". He also accepts "the bona fides of the Sinn Féin leadership regarding their rejection of violence and pursuit of the peace process, and I accept their assurance that they want to support police in bringing those responsible to justice".

That's all quite benign It is. Indeed, the former minister for justice Michael McDowell said the British and Irish Governments were content that the IRA could be maintained as an "unarmed and withering husk" that would dampen the impact of the dissident republican threat.

But we're back in crisis. Is Stormont doomed? We're seldom out of crisis. The bottom line is that two men were murdered, one allegedly by IRA members, even without the authority of the "hierarchy". And the chief constable said the IRA still exists. The Ulster Unionist Party leader, Mike Nesbitt, is withdrawing his single Minister, Danny Kennedy, from the Northern Executive because unionist trust in Sinn Féin is "shattered". The pressure is on Peter Robinson and the DUP to follow suit. If they exit Stormont, it could result in suspension of the Executive and Assembly, possible Assembly elections, and an indeterminate period of British direct rule.