Agreeing to a backup plan for solving the Irish border dilemma is a condition of moving ahead. If it can be done, Mrs. May can probably fudge her plans for future trade, compromising on her Chequers proposal but leaving things vague and then negotiating the details in a 20-month “transition period” during which nothing much will change for Britons.
But if Ireland cannot be fixed there will be no “transition period” and a cliff edge departure looms. That could mean trucks marooned in port, stores running out of some kinds of food and some factories deprived of the components that arrive each day from continental Europe.
When Mrs. May and Mr. Varadkar met on Thursday, British news outlets reported, the British prime minister told her Irish counterpart that the latest in a slipping set of deadlines for agreement on Ireland’s backstop — a summit meeting in October — was likely to be missed.
With that, European Union leaders seem to have concluded that Mrs. May was once again trying to delay things, ramping up fears of a no deal, and hoping to force them to soften their stance as Brexit day in March draws closer.
So instead of playing along and saying noncommital things about her Chequers plan, they plotted an ambush, disparaged central parts of it and demanded significant progress on the Irish border at a meeting in October. Without that, a further summit meeting to finalize Brexit, penciled in for November, would be canceled, they said.
For now, the European Union side seems content to sit and watch the fallout from what some see as a cathartic moment in British politics. From the tenor of her remarks on Friday, Mrs. May is sticking to her Chequers plan although it has already prompted two resignations from her cabinet and has been pronounced dead by her critics.
Most experts agree with Mr. Tusk that her plan is unworkable, at least in the short term. Its real use was as a starting point for talks and as a theoretical long-term solution to the border question — a fig leaf that could allow Mrs. May to agree to a backstop plan for Northern Ireland but also suggest it would never be needed.
That convenient fiction has been undermined by Mr. Tusk’s brusque remarks, making it harder for Mrs. May, whose enemies within her own party are sharpening their knives.