Suzanne Breen: May now facing some very tough decisions
When the DUP fought the 2017 Westminster election, it could not in its wildest dreams have hoped to be in the staggeringly powerful position it currently occupies.
The party's 10 MPs last night saved the Prime Minister. Had they supported Jeremy Corbyn's motion of no confidence, Theresa May and the Tories would have gone down by a single vote.
As Arlene Foster was swamped by camera crews in College Green, opposite Parliament, it appeared - last night anyway - that she, and not Mrs May, was the most influential woman in the UK.
The two women held a meeting yesterday which the DUP described as "useful". But the key to the future relationship between their parties will depend on what path the Prime Minister now takes as her Brexit plans lies in tatters.
The choice is clear. She can reach out to Labour and the Opposition parties by opting for a softer Brexit involving customs union membership or she can try to reach a compromise with the DUP and European Research Group (ERG) MPs.
Clearly, the former option is the route that some Cabinet members and senior Remain Tory MPs would like her to follow.
But it would be absolutely disastrous for the Conservative Party. The resignation of a range of ministers and dozens of Brexiteer MPs would surely follow.
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Mrs May's loyalty and love for her party makes it highly unlikely she would choose any course of action that would result in such a historic split.
But if she did seek to build such a cross-party coalition, it would be potentially disastrous for the DUP. The party is savvy enough to know that no matter how high it is now riding, there are still pitfalls a plenty in the current political landscape.
The DUP's opening position is that the backstop be binned but Mrs Foster has indicated that a time-limited backstop which doesn't undermine the Union could be acceptable.
But critics believe there is zero chance of Brussels agreeing to such a proposal, and that is why Mrs May will ultimately be forced to seek a coalition with Opposition Remainers. The only other solution for the Prime Minister is to take the initiative and herself call a snap election as a way of breaking the deadlock.
Yet that too involves massive risks. The last time she threw the political pack of cards in the air in an attempt to strengthen her position was in April 2017. And we all know how that ended.