Arlene Foster's departure inevitable
Although the timing of the challenge to Arlene Foster's leadership came as a surprise, her departure as DUP leader has been inevitable for some time.
Her handling of RHI, her apparent inability to impose party discipline and her failure to plan for the consequences of Brexit have significantly damaged party support in the face of next year's assembly election.
The fear of electoral collapse has triggered collective panic among DUP MLAs, most of whom believe that a change at the top will reverse the party's decline. Whether a new leader can significantly transform the DUP's fortunes remains to be seen.
A significant problem for the party has been its inability to chart a clear path for development as a major force in northern politics. Instead it has spent considerable energy reacting to events rather than shaping them.
That reaction has been largely inconsistent, as illustrated by the party's initial acceptance of the Northern Ireland Protocol and its later rejection of it in the light of loyalist street protests. This highlights the party's disconnect from what has been its support base since its foundation.
While the contenders for Mrs Foster's position are still a matter of speculation, the style and content of the new leadership will have significant implications beyond the DUP.
It will shape not just the party's electoral performance, it will determine the assembly's future, influence the role of North-South bodies and define unionism's relationship with London.
Addressing these issues requires the development of a coherent political philosophy for the DUP. It must find a way to balance its fundamentalist religious tradition with the demands of being in an inclusive system of government.
Mrs Foster's often inconsistent leadership certainly contributed to the DUP's difficulties, but her underlying problem was that she was also required to articulate a broader and more positive concept of unionism in a rapidly changing social and political environment.
It was a difficult challenge which proved beyond her.
Whoever succeeds her will find that same problem in the party's in-tray. The new leader's handling of it will determine not just the DUP's future, but the nature of politics across the whole island.
So what is a leadership selection issue for the DUP may prove to be a pivotal moment in history for the rest of us. It is a selection which needs to be handled wisely.