There might still be ways that Brexit can go badly; unexplored dead ends and byways of failure. But the road to success is now closed. Parliament’s second verdict on Theresa May’s deal is slightly less crushing than the first one in January. But a defeat by 149 votes, just weeks before Britain is due to leave the EU, indicates not only the last evacuation of any authority from the prime minister but a profound crisis in the project that is the only purpose of her government. She had one job, and she cannot do it. Vital questions about the future will now be settled in a state between despondency and panic. There is no strategy, no guiding intelligence. A plan must be salvaged from the wreckage of a bad idea badly executed.

MPs ignore May’s pleas and defeat her Brexit deal by 149 votes Read more

There was a moment, early on Tuesday, when May thought she saw a way through. A path was briefly visible to the promised land of orderly Brexit. The prime minister had brought legal clarifications from Strasbourg to embellish her deal. But then the road was barred by Geoffrey Cox. The attorney general judged that the UK might still find itself in the notorious backstop – an EU customs union – with no unilateral means of dissolving the arrangement. Indefinite backstop is a deal-breaker for hardliners.

Cox’s judgment spread disappointment well beyond the circle of noisy Brexit ultras. There is a quieter tranche of MPs whose first preference is that Brexit just be done with a minimum of trauma. Most aren’t that bothered about the detail. But May’s withdrawal agreement, the only existing mechanism to achieve their goal, is just too toxic after so much high-profile scorn.

Pro-Brexit Labour MPs need Tories to vote for a Tory deal. Many Conservatives wanted to oblige, but they needed a credible reason to endorse something in March that they had despised in January. A revision of the backstop was meant to be the ladder down which they could climb with dignity intact. Instead the prime minister asked them to make an awkward leap on her behalf. Not enough Conservatives trust or like their leader enough to do that.

That was always going to be a political calculation, not a legal one. The story that May’s deal, sprinkled with magic codicils, could be transformed from a dud to diamond was dishonest. The Brexit ultras of the European Research Group put on a show of legal piety, convening a “star chamber” of jurists to evaluate the EU’s offer. They borrowed the nomenclature from Tudor England, not because the historical analogy is appropriate but as a stylistic affectation, lending bogus gravitas to what is, in reality, a conclave of veteran Eurosceptics who were always going to say what decades of prejudice had primed them to say: that Brussels has not given enough; that the sovereignty of Albion is affronted.

I do not recall the high priests of Brexit being so interested in legal nicety when arguing that Britain should quit the EU without a deal, reneging on financial commitments already made under the December 2017 “joint report”, and hang the consequences for Ireland and its border. In the referendum, leave campaigners were hardly fastidious in explaining the technical implications of ending UK-EU treaties. They didn’t even feel bound by domestic electoral law, as subsequent investigations have established.

Britain did once cultivate a sober, lawyerly and realistic strain of Euroscepticism. The perspective it brought to EU affairs, the laconic distance from continental flights of federalism, was often appreciated by fellow member states. It was a valued part of the cultural mix. But that trait has been submerged in a torrent of romantic nationalism that sweeps rational query aside and dismisses practical objections as deficient patriotism.

Every difficulty encountered in Brexit negotiations over the past two years was foreseeable. Most flowed from the same essential miscalculation: the wildly implausible expectation that a bloc of 27 nations, each knowing the value of unity and solidarity, would be the weaker party in negotiations. The path to May’s humiliation began in the weird solipsism of an exiting country, having no notion of the relationship it wanted with the rest of Europe, imagining it might dictate the terms of its exit.

Play Video 0:43 MPs reject May's Brexit deal for second time by majority of 149 - video

Brexiters cite their technical reasons for hating the backstop, but it also represents something so painful that they dare not admit it, even to themselves. It exists because European nations resolved to put the needs of Ireland, a small country, ahead of demands by the UK, a bigger, mightier country. It is an emblem of the protection that EU membership affords. It proves that national power can be amplified in Brussels, when Eurosceptics insist it can only be debilitated there.

All of the diplomatic and political wrangling over the past 24 hours – and many Westminster skirmishes over the previous 24 months – have been little more than displacement activity for the Tories. There have been countless excuses to fuss around in the undergrowth of the Brexit process just to avoid looking up at the horizon and blinking in shock to see the world as it is, not as the leave campaign falsely promised it would be.

This has been the greatest source of frustration and shock for the rest of Europe: the spectacle of a once serious country, formerly admired for the coolness of its temperament, racing towards perilous choices while turning its face defiantly against obvious realities. That, plus the tragic irony of history creating a vacancy for visionary leadership and then filling it with May.

There is an almost perfect mismatch between the prime minister’s character and the skills she has needed. She was blunt when she should have been diplomatic; inscrutable when she needed to be candid. When imagination was required, she opted for inane repetition. When she should have reached out, she doubled down. She appeased enemies of compromise in parliament and squandered goodwill in the country.

It can be hard to disentangle the disaster Brexit might always have been from the specific mess May has made of it. There are turnings on the road to failure that she did not need to take, junctions that were missed. She did not have to embark on the article 50 route before knowing where it led. She could have drawn different red lines or changed them when they confined her to impossible choices. But while there were problems with the driver, there were also limits to how far she could get with Brexiteer maps, scrawled in crayon on the eve of the referendum with wild, higgledy lines pointing at destinations that don’t exist.

The result is that the country has been driven round in circles. The parliamentary debate on May’s deal today was a gloomier, paler version of the one that was held in January. For much of the day the Commons benches were emptier than last time. The prime minister’s exhausted voice was hoarser. The deal was rejected by a smaller margin not because it has got any better, but because fear and exhaustion are catching up with Tory MPs, overtaking their belief that something better will come along.

As for the implacables who voted against May, they were not jubilant. They inflicted a defeat, but they know also that there was no victory here for any kind of Brexit. A ruinous no deal is still technically possible, but a chain of events has been triggered that could lead to postponement or even annulment of the whole project. The prime minister’s humiliation could rebound on to every Eurosceptic fanatic who urged her ever further and faster down the road to nowhere. Brexiteers have a dangerous adversary that they cannot name. It isn’t any opposition party, or Brussels, or remainers. It is reality.

• Rafael Behr is a Guardian columnist