LONDON — Like a stumbling figure from “The Walking Dead,” Britain’s prime minister, Theresa May, has yet to realize that she is a political zombie. For all her poise as she spoke on Downing Street on Friday, the day after Britain’s general election, when she declared her intention to continue in office, she is roaming the land of the undead. Sooner or later, reality is going to bite — hard.

Once again, almost all the pundits, pollsters and political betting wonks got it wrong. Less than a year after Brexit stunned this country, and seven months after Donald Trump won in the United States, a political outcome that seemed certain and preordained was upset by people actually going to vote. They made an emotional pick, and now Mrs. May has to figure out what to do after a net loss of seats in the House of Commons that deprives her of the overall majority required for stable government.

As the extent of the upset became clear on Thursday night, it was assumed — even by many of Mrs. May’s most ardent supporters — that she would be gone by Friday morning. There was talk of a “dignified exit,” a timetable for departure and then, unavoidably, another general election. Instead, Mrs. May has formed a pact with Northern Ireland’s Democratic Unionist Party, an alliance that will give her an aggregate number of members of Parliament that passes, just, the 326-seat threshold required for a governing majority.

Doesn’t this suffice? Surely a politician is entitled in such circumstances to be creative, if only to deprive her opponents of power?

I have praised much that Mrs. May has done as prime minister: uniting a party torn apart by the European Union referendum last year; triggering the Brexit process in Parliament after a supreme court challenge; and, most laudably, seeking to extend the reach of her party from the affluent to those who are, in her own phrase, “just about managing.” In her unfairly criticized manifesto, she eschewed glib slogans and confronted issues of great and pressing complexity, such as the care of the elderly in a country with an aging population, the pathologies of the internet and the grievances of those left behind by the hectic forces of globalization and modernity.

So why not salute her gutsy decision to carry on? The problem is twofold. First, Mrs. May explicitly framed the election — which she was not obliged to call when she did — as a test of her leadership, character and credentials to negotiate a good Brexit deal with the European Union. Posturing as a statesman being undermined at home by amateur politicians, she demanded a clear mandate from the voters to crush her opponents and demonstrate to European leaders that she was backed unequivocally by the British people.

Well, the British people have spoken — and conspicuously withheld that backing.

In a race against a supposedly unelectable hard-left leader, Jeremy Corbyn — whose own Labour Party members of Parliament tried to topple him last year — Mrs. May lost seats. Though Mr. Corbyn failed to win the election, he has made significant gains. He has not only secured his own position, but also, extraordinarily, has established his Castro-loving, Chávez-friendly brand of socialism as the mainstream creed of the party that, only 10 years ago, was led from the center by Tony Blair.

This election campaign was twice interrupted by horrific terrorist attacks, first in Manchester, then in London. Inevitably, this put security at the heart of the race, and shone an unflattering light on Mr. Corbyn’s past links with the Irish Republican Army and his opposition to antiterrorism legislation. For days, before the election, Britain’s tabloid press was crammed with lurid details of his coterie’s alleged associations with paramilitary and Islamist organizations.

But none of this made the slightest difference in the outcome. Or, put another way, none of it did Mrs. May any good. In the early stages of the campaign, some of her supporters privately admitted that she had called this snap election for fear that Labour would ditch Mr. Corbyn later in the year and deprive the Conservative Party of an opportunity for a landslide victory.

Mrs. May took that shot, and missed by miles. Her decision to cling to power now looks undignified; that is out of character. Moreover, her alliance with the unionists looks like an act of desperation. It is.

From 2010 to 2015, the Conservatives (then led by David Cameron) governed in coalition with the Liberal Democrats under Nick Clegg (who lost his seat in this election). That alliance, long-planned and carefully choreographed, was hard enough to maintain, even with plenty of common ground between the center-right Tories and their center-left partners.

The Democratic Unionist Party, in contrast, is a hard-line reactionary party, devoted not only to the union of Britain and Northern Ireland, but to a social conservatism that directly contradicts the modernization of the Conservative Party in the past 15 years. When she was the party chairman from 2002 to 2003, Mrs. May did much to brush away the cobwebs, daring to tell annual conference delegates that theirs was perceived as “the nasty party.” Now, nearly 15 years later, she has allied it with the Even Nastier Party.

How will she explain to the socially liberal, centrist voters whom Mr. Cameron won over during his decade-long leadership that she must now govern in partnership with a group of homophobes, zealots and creationists?

Mrs. May might claim that it is her duty to form a government, given the alternative: some improbable Corbyn-led rump of Labour plus the Liberal Democrats and the various nationalists. But that alone is not sufficient justification for this shabby deal, which will only confirm the suspicion that all the Conservatives truly care about is power.

Worse, Mrs. May has failed to acknowledge the scale of what has happened, or even that it has happened at all. Whatever one thinks of Mr. Corbyn’s credentials and record, he tapped into a popular anger and a yearning for change, as the Brexiteers and Mr. Trump did. He understood how to achieve emotional resonance and, most impressively, inspired young people to vote.

If Mr. Corbyn never really looked like a prime minister-in-waiting — someone who could run the Civil Service, craft detailed public policy or handle the nuclear codes — there, counterintuitively, lay his appeal. The insurgent populism of 2016 has not gone away. Here, it took a new, left-wing form.

I see little sign that senior Tories have grasped how radically the rules of the game are changing around them. It has now been 30 years since the party won a solid majority, and in apparently ideal conditions, it failed to do so in this election. What sharper wake-up call do Conservatives need?

The new government, Mrs. May said on Friday, provides “certainty.” She is right, but not in the sense that she meant. Its parliamentary majority is certain to be under constant attack from rebels of all kinds. Its weakness is certain to be mocked in Brussels, as the Brexit negotiations begin. And it is certain, sooner rather than later, to collapse, as such fragile arrangements always do. These extra months that Mrs. May remains in power will be grueling, unproductive and harshly judged by posterity.

As an admirer of Mrs. May, I wish she had chosen to leave with honor intact, instead of subjecting herself, and the country, to the ordeal ahead. The party is well and truly over. Will someone have the grace to tell her?

(The New York Times)