Sam McBride: Foster's future no longer secure, but she is still likely to survive

Even with the scale of the current crisis, such a scenario is still unlikely. But it is no longer unthinkable.

Mrs Foster retains enormous support within the DUP and there are scant indications of any significant internal move against her.

By contrast to her predecessor, Peter Robinson, who had under his belt a host of crises and myriad enemies, Mrs Foster is still a fresh leader with a relatively clean slate.

And – crucially, given that it is the DUP Assembly group which elects the leader – she is particularly popular within that segment of the party, not least because her stunning electoral success in May’s election saw all 38 MLAs retain their seats when several feared for their futures.

By contrast, Jonathan Bell was not a popular figure within the DUP even before his spectacular full-frontal assault on its key leadership figures, both elected and unelected.

Nevertheless, Mrs Foster is arguably facing a greater crisis than that which enveloped Mr Robinson after the BBC Spotlight revelations about his wife, Iris.

By contrast to that situation – which, aside from his wife’s affair, centred on the relatively small sum of £50,000 from two property developers – Mrs Foster is accused of having been central to the construction and oversight of a scheme responsible for waste on an astronomically larger scale.

The consequences of £400 million being stripped out of budgets for hospitals, schools and roads over the next 20 years are easily understood by voters and highly emotive.

It now seems clear that there will be some form of independent inquiry. At this juncture, the critical decision is what form that takes. There is precedent from Peter Robinson’s era of a QC being brought in to give a legal opinion on the situation – essentially the weakest option, operating behind closed doors and (as in the case of Mr Robinson) the legal opinion may never be published.

At the other end of the scale, a judge-led public inquiry set up under the Inquiries Act would be in public, would have the power to compel witnesses and papers (including bank statements) and would, if it cleared Mrs Foster, allow her to conclusively put this episode behind her.

There would be a cost – perhaps more than a million pounds, if hearings were to last for months.

But, given the scale of the squander in this case and the imperative for getting to the truth, that now seems like a reasonable price to pay for restoring confidence not just in the First Minister but in all of Stormont.

But that decision is for the DUP and Sinn Fein to take. The DUP’s clear reluctance for such an inquiry and Sinn Fein’s warm relations with Mrs Foster’s party over recent months mean that a less far-reaching form of probe is likely to ultimately be deemed sufficient.