No sooner had Prime Minister Theresa May unveiled her 585-page draft of a deal on withdrawing from the European Union than all hell broke loose. Ministers resigned, hard-core Brexiteers began stirring up a leadership challenge; in the House of Commons, Mrs. May’s talk of a “smooth and orderly” divorce drew prolonged hilarity followed by a three-hour assault on her plan from every bench — Leavers, Remainers, Labourites, Liberal Democrats, Northern Irish, Scottish Nationalists.

In the bitter saga of Brexit, each formidable hurdle has been followed by an even greater one. So it is now: If Mrs. May survives this onslaught, and if the agreement is approved by the union, the deal must return for a vote in Parliament, where current tallies are heavily against it. The prospect of Britain exiting the union at the March 29 deadline without a deal, the worst of all possible outcomes, looms large. That, almost everyone agrees, would be a disaster for the British economy and security. It would mean tariffs and border checks, miles of backed-up trucks, businesses in flight, supply chains choked and other woes galore.

Yet as the members of Parliament took turns denouncing Mrs. May’s plan, none had a better idea. The reason for that is simple — there is no plan that would allow Britain to have its cake and eat it, too, as disingenuously promised by Boris Johnson, the former foreign secretary and most shameless of Brexit propagandists.

From the outset, British politicians have debated Brexit as if they have the decisive say in the outcome, while Mrs. May has been compelled to deal with a European Union that actually does have the final word on the conditions under which Britain would retain access to the bloc after it withdrew. That is not to say the European Union is indifferent to the outcome — a deal-less exit would have severe repercussions on the Continent as well. But European Union officials in Brussels were never prepared to let Britain pick and choose among the benefits, costs and obligations it would keep or shed.