How did it come to this? How could a politician hailed for her courage and tactical acumen a year ago be spending this weekend holed up in Downing Street, friendless and widely ridiculed, a prisoner of her furious party and of events that have spun out of her control? How could someone who just days ago was confidently preparing to fulfil her ambition to guide Britain into its new role abroad and refashion its institutions at home be now preparing for the humiliation of resignation from her post that must surely happen soon? How could a prime minister who seemed imperious just weeks ago when she set out to destroy Corbyn’s Labour be laid so low, the power draining from her as her backbenchers and senior cabinet ministers make demands she is too weak to resist? Whatever happened to “strong and stable”, parroted to the point of banality by May and her senior colleagues throughout the campaign. Whatever the position of Theresa May three days after the election, it is not strong and it is not stable.

The prime minister presided over one of the worst election campaigns in history. She squandered a 20-point poll lead and her parliamentary majority. The contrast between the prime minister of last July and the prime minister we saw on Friday could not have been starker. Then, she stood outside Downing Street claiming to be a leader attuned to the people, who understood the European referendum vote as a demand for a different sort of politics. The day after the election, she was the leader we have come to know in recent weeks: inflexible and wooden, unable to acknowledge her defeat, she came across as deaf to the message that the nation had just delivered.

May called this election as a vote of confidence in her vision. She expected to win a mandate for her hardline approach to Brexit and her programme of austerity easily. Instead, she lost seats. She has no mandate for either. The result should put paid to her ruinous claim that no deal with Europe would be better than a bad deal. It should sound the death knell for the public spending cuts she championed, despite the pain it has inflicted on countless lives.

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Despite a campaign pitch based on her leadership qualities, May avoided media appearances, debates and contact with the public wherever she could. Her message was framed not around a positive vision, but around vicious personal attacks on Jeremy Corbyn. She sought a mandate for her Brexit strategy without providing any elucidation of what it would be.

Her campaign was memorable for its strategic errors on domestic policy and she offered no answers to the big questions facing Britain, including the plight of a younger generation locked out of the proceeds of prosperity. Despite enacting changes to the tax and benefit system that leave low-income families thousands of pounds a year worse off, she claimed to be fighting their corner. Instead of bringing the country together after the Brexit vote, she launched an attack on “citizens of nowhere”. There were enough who saw her for what she is: disingenuous, dogmatic, unstrategic.

May lost her election gamble, but Jeremy Corbyn unexpectedly played a critical role in denying her an outright victory. His campaign was widely acknowledged as exceeding expectations in the run-up to the election, but the result shows how successful it was. He confounded his critics to secure the largest increase in the party’s vote share since the second world war to take Labour to 40%.

Corbyn has done what many of his critics thought would be impossible. He built on the enthusiasm inspired by his leadership election to attract support from young voters far beyond his membership base, building them into an electoral coalition with metropolitan voters and Labour’s core working-class vote. His was a strategic campaign that blended a popular policy platform with a pragmatic position on Brexit that enabled him to keep Leave-supporting voters within the Labour fold. And he did this in the face of an overwhelmingly hostile media climate and in spite of being vastly outspent by the Conservatives. The rightwing press were skilfully outmanoeuvred by Labour’s digital activists. Their increasingly hyperbolic front pages went unseen by the under-30s and, counterintuitively, to those who did see them, they helped create support for an besieged underdog. The Mail, for the first time in a while, seemed out of touch with a seismic movement in politics. After a year of bilious cant against Remainers and Corbyn, it was left firing analogue bullets in a digital age.

It may be short of a win, but it remains a sensational result for Labour and cements Corbyn’s position as leader of his party. He has led Labour to a position where, if there were another general election later in the year, victory looks far from impossible. He has responded to the growing crisis that has beset our political institutions since the 2008 financial crisis in a bold and imaginative way, engaging a new generation that had found little inspiration in the existing political establishment. He has harnessed the anger of the dispossessed as well as the energy and optimism of the young. He successfully punctured some of the cynicism that has descended over British politics.

But Thursday’s result leaves the most important question unanswered. Who now has the authority to govern Britain? We stand on the brink of the most important international negotiation since the Second World War, led by a prime minister lacking in authority and political capital. May’s decision to trigger article 50, and then call an election, was catastrophic. It is the second time in two years a Conservative prime minister has risked Britain’s national interest for personal political advantage and party management.

The two-year clock on a transitional deal continues to tick. But our politics looks as though it will be gripped by paralysis in the weeks to come. There now exists a majority of MPs in parliament in favour of a softer approach to Brexit. But the erosion of her majority means May will undoubtedly be held hostage by her party’s Eurosceptic right. It is impossible to see how this can resolve itself.

This election result also adds instability to the union. The SNP’s significant losses mean the Scottish independence question is settled for now. But things look less assured in Northern Ireland, where the collapse of power sharing has created a fraught situation.

This election saw the wipe out of the moderate unionist and nationalist parties. Sinn Fein’s absence means only the hardline unionist DUP will be represented in Westminster, leaving nationalist voters in the province with no voice. As Jonathan Powell writes on these pages, any deal May strikes with the DUP will overturn the convention that the British government is neutral between unionists and nationalists. How could May claim neutrality if her government is propped up by the DUP’s 10 MPs? In reaching out to them, May is jeopardising the peace brought about by the Good Friday agreement.

One of May’s most prominent attacks on Labour was that a vote for Corbyn was a vote for a coalition of chaos. There is a terrible irony in the fact it is now May who will be forced to rely on an agreement with the DUP in order to govern. Members of a party rooted in conservative Christianity, the DUP’s MPs are some of the most reactionary, socially illiberal voices in parliament. Anti-gay marriage and anti-abortion, the party counts creationists and climate change deniers within its ranks. Any alliance with the DUP would be at odds with efforts by Conservatives to shed their image as the nasty party.

May finds herself in an impossible position. She must respond to the electorate’s rejection of austerity and hard Brexit. There are moderates in her party who will demand it of her. But those to the right of her will try to prevent her from doing so. This election result calls for a far more open style of governing. There is a need to build a coalition in the Commons for a Brexit deal that puts Britain’s economic prosperity first: the obvious arrangement would be continued membership of the single market. Yvette Cooper’s proposal for Brexit talks to be led by a cross-party commission with the Brexit secretary at the helm deserves consideration.

Discredited, humiliated, diminished: May has lost credibility and leverage in her party, her country and across Europe. Where there was respect, there is ridicule; where there was strength, there is weakness; where there was self-assurance, there is doubt. She looks too weak to deliver her manifesto, too vulnerable to tackle dissent and too enfeebled to lead Britain. It is impossible to see her having the influence, authority or credibility to serve her country.