This morning on BBC Northern Ireland’s Sunday Politics a tetchy Arlene Foster was asked about Steve Aiken, the leader-in-waiting of the Ulster Unionists.

Yesterday, on the morning of a subdued DUP conference - arguably the party’s trickiest in years - Aiken used a Belfast Telegraph interview to rule out any cooperation with his party’s much bigger rival come the next general election.

That openly confrontational stance is no surprise: Aiken, a Remainer who is firmly situated on the more liberal wing of the UUP, clearly believes there is electoral hay to be made in attacking Foster’s party - and he has done so vociferously as its woes at Westminster intensify.

But it does mark a significant shift in the UUP’s electoral priorities. Despite their differences with the DUP, under past leaders they have ultimately been willing to put the election of a unionist over a nationalist above partisan pride.

In practice, that has meant standing aside in seats like North Belfast, where the DUP’s Westminster leader Nigel Dodds is defending a slender majority over Sinn Féin.

So it was telling that Foster, quite unprompted, chose to cite that very example when asked about Aiken’s new gambit this morning:

“Right across unionism, people will be despairing at Steve Aiken today. The fact is that he is prepared to put in jeopardy seats and allow them to go to Sinn Féin. “I think he is the one that needs to reflect one what exactly he is trying to do. It's telling, it's very telling that his first interview says there won’t be any electoral pacts. “I presume that means in North Belfast, where there is a possibility that Sinn Féin will take the seat. I presume that means Fermanagh and South Tyrone, where if there is not a pact, that seat will go back again to Michelle Gildernew. “So here we have a man who claims to be a unionist leader, who thinks it’s okay to hand seats back to Sinn Féin.”

It is a striking - and uncharacteristic - admission of electoral vulnerability. And it is also a high-stakes gamble. Foster is betting that, when push comes to shove, Aiken will fold and step aside rather than risk such a symbolic loss for unionism in North Belfast - and potentially forfeiting his only realistic chance of winning an MP in Fermanagh and South Tyrone, where it is the DUP who tend to stand aside for the UUP.

Given that he is already staking his leadership - and with it his party’s survival - on attacking the DUP, there is no guarantee that Aiken will play ball. To do so would be to undermine what he believes to be his unique selling point. But his predecessors, most notably David Trimble and Mike Nesbitt, learned the hard way that the UUP grassroots are often uneasy (often noisily so) about anything that aids the republican or nationalist cause, however indirectly.

Yet for Foster to assume that Aiken will not risk doing things differently is to engage in a game of brinksmanship that could leave her party much diminished at Westminster after the next election.