LONDON — Brexit is a rose with a lot of thorns. It offers politicians a precious resource: the ability to claim they are representing the will of the people, as expressed in the 2016 referendum. But it carries a price. It is almost impossible to deliver while keeping the whole disparate coalition of people who support it on board. Whenever it moves from rhetoric to policy reality, it pricks their fingers.

Boris Johnson is currently discovering this firsthand.

He managed this month, despite rock-bottom expectations, to secure a new deal with the European Union — one that allows Britain to distance itself from the continent and seek trade deals elsewhere, especially with the United States. It would slice the United Kingdom’s customs territory in two, leaving Northern Ireland behind in a customs ecosystem with Europe. That meant Johnson lost the support of the Democratic Unionist Party, the fiercely pro-Union, fire-and-brimstone Northern Irish party that had put the Conservatives in power after they failed to win a majority in Parliament on their own. There were other advantages, though: He could persuade the hard-liners in his own party, who had opposed all previous incarnations of Brexit as insufficiently radical, to go along.

So with a deal in hand, Johnson unleashed the full rhetoric of the “will of the people” against his opponents. To oppose the deal, raise concerns about it or even ask for it to be properly scrutinized was to undermine the electorate. To support him was to support Britain. This is the populist register in which the Brexit debate is conducted. And it is still punishingly effective against many members of Parliament, even three and a half years after the referendum. With an Oct. 31 deadline looming as a threat — that Britain would leave Europe with no deal if Parliament did not approve Johnson’s plan — Johnson expected to get his way.

Parliament voted Oct. 22 to support Boris Johnson’s Brexit deal in principle but rejected the prime minister’s timetable for passing it in the next three days. (Alexa Ard/The Washington Post)

Instead, Parliament rebelled again. Johnson wanted them to vote on just a one paragraph motion saying they would accept his plan. Instead, they demanded to see the full legislation of what it entailed.

And this was the nightmare scenario for Johnson: Not only would it delay matters, it would also force him to reveal the details of his plans.

Johnson is not really a details man. When he was foreign secretary, he inadvertently reinforced the Iranian case against an imprisoned British citizen, Nazanin Zaghari-Ratcliffe, telling a Commons committee she was “simply teaching people journalism” — the exact claim made against her by prosecutors. When he was running to be Conservative leader, he rested one of his central arguments on article 24, paragraph 5b, of the General Agreement on Tariffs and Trade, only to then admit he had no idea that paragraph 5c negated it.

But even if he had greater mastery over the details, there was a larger problem: Brexit functions only when it has no contact with reality. The referendum campaign was won by telling well-off golf club voters in southern England that they had the same enemy as the left-behind voters in the postindustrial towns of the north. At the level of rhetoric and blame-the-foreigner sloganeering, it works. But when you try to formulate it as a coherent policy proposal, the whole thing falls apart.

The same applies to Parliament. The coalition Johnson needs to stitch together involves hard right-wing Brexiters, moderate Conservatives — most of them now purged from the party for voting against Johnson — and left-wing Labour MPs with Leave constituencies. They all want to get Brexit done. But once you get down into the reality of what it entails, the alliance disintegrates.

Labour MPs want the E.U.’s workers’ rights and environmental standards kept locked in place. Hard-line Brexiters want them gone. Moderate Conservatives want protections against another no-deal cliff edge in December 2020, when the transition period in Johnson’s deal would end. Hard-liners want to use that date to tear Britain out of the E.U.’s orbit in one satisfying wrench.

Despite all his efforts to stop it, the amendment insisting on the full legislative text of the plan squeaked through. The government was on the back foot again. Because Parliament had not approved the deal by 11 p.m. last Saturday — a date that had been set in law last month, during a previous parliamentary rebellion — Johnson was forced to request yet another deadline extension for Britain’s departure.

In an act more suited to a recalcitrant schoolboy than a prime minister, he refused to sign the letter he sent to European leaders requesting the delay, and then he attached other documents insisting he opposed it. His counterparts on the continent must have looked at the communication in bemused despair. They were essentially negotiating with two Britains: its legislature and its executive, acting as fully independent political entities. But legally, it did not matter. The letter was sent. The condition for extension was satisfied.

So Johnson adopted a new tactic. He knew he had a few days until the E.U. responded, so he published the full legislation on Monday — 435 pages of legal text and supporting documentation — and then demanded MPs vote on it by Tuesday, with all further stages to be sorted out by the end of the week. If he had to publish the details, he could at least make sure no one had time to read them.

This was unprecedented. Previous pieces of legislation affecting Britain’s constitutional arrangements had taken months. Even the Wild Animals in Circuses Act, passed earlier this year and affecting a grand total of 19 animals, had been given 11 days.

The legislation still cleared its first hurdle Tuesday night, when MPs voted to approve the principle of the bill. But Johnson’s victory lasted only a few minutes. Less than half an hour later, MPs voted down his timetable.

That detonated his plans. Without the quick timetable, he would be unable to avoid pushing the deadline to leave Europe back. And if there is an extension, MPs would have plenty of time to read over the deal before deciding if they supported it. Now European leaders are expected to set the new deadline to Jan. 31. His only chance is that French President Emmanuel Macron comes to his rescue and demands a shorter time frame.

Johnson is standing in the rubble of his strategy. He cannot rush a deal through, and he cannot avoid its details and all the contradictions they entail.

There are now two possibilities for the next few weeks. Either the bill takes longer to go through Parliament and becomes caught up in a tug-of-war between opposed pro-Brexit factions, or Britain will hold a general election in which the prime minister tries to convince the country of the deal’s merits.

The numbers are — just about — in his favor. He has a slim majority for the deal in Parliament and a decent polling lead in the country. But he is now in the place to which he is least suited and where Brexit dreams go to die: objective reality. He is in the treacherous terrain of policy detail, in which the dense technical translation of that all-things-to-all-people Brexit campaign is written down in black and white.

A politician who defines himself through poetry is about to have to campaign with prose — or worse, try to govern. It will not be a pretty sight.

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