LONDON — There is a genteel savagery to the British prime ministerial system. If you blinked last week, you’d have missed David Cameron’s exit and the arrival in No. 10 Downing Street of Theresa May. No period of transition separates one regime from the other, allowing the nation to acclimatize to its new head of government. One prime minister is hustled out No. 10, and another is hustled in.
Though British politics has grown increasingly presidential, ever more focused on the personality of the prime minister, its system remains parliamentary, and the party that commands a majority in the House of Commons chooses the prime minister. Last week, Mr. Cameron was driven out by his defeat in the European Union referendum, only 13 months after winning a general election. The slender majority of parliamentary seats that he achieved as leader of the Conservative Party is inherited by his successor, Ms. May. In theory at least, the mandate belongs to a party, not a person.
The new prime minister was the home secretary for Mr. Cameron’s entire six-year term. Throughout, she positioned herself discreetly for a run at the top job, occasionally raising her profile with a speech that ranged outside her regular policy portfolio. She not only wooed the party’s right wing with pledges to cut back immigration, but also courted the “modernizers” who believe that the party must reach beyond its base with her commitments to same-sex marriage and racial equality.
After the Brexit vote, the news media and the Conservative Party were all prepared for a battle between George Osborne, the chancellor of the Exchequer, and Boris Johnson, the former mayor of London. In the event, neither entered the race, which Ms. May won with ease.
Those who expected her to offer respectful continuity were immediately disabused of the notion. Ms. May’s first act was a ruthless reshuffle of her predecessor’s team. Out went Mr. Osborne, apparently too associated with the ancien régime for the new prime minister’s liking. Out, too, went Michael Gove, the former justice secretary. He would have been an asset but, in Ms. May’s judgment, could not sit at the same cabinet table as Mr. Johnson, her newly appointed foreign secretary. (The two had been allies in the pro-Brexit campaign, but Mr. Gove dramatically ended that alliance when he ran for the party leadership himself, ruining Mr. Johnson’s chances.)
Even the most seasoned analysts of British politics were struck by the brutality of Ms. May’s hirings and firings. This was no accident: The prime minister wanted to send a clear signal that she represents change, not the status quo. This was intended to be a shock to the system; the new prime minister wants to be seen as a Tory radical rather than a caretaker of Mr. Cameron’s legacy.
Her leadership will be turbulent, whether she wants it to be or not. Her primary task is to carry out the result of the referendum and ease Britain out of the European Union with the best possible deal. Although she was a nominal Remain campaigner, her slogan since the vote has been “Brexit means Brexit.”
This naturally disappoints those Tory members of Parliament — perhaps a majority — who still hope that the practicalities of leaving the union will be prohibitive, and that a second referendum (or a general election in which continued European Union membership is a central issue) might yet thwart an exit.
Not a chance. Prime Minister May has in effect staked her reputation on delivering a comprehensibly advantageous solution to this hugely complex problem.
At present, Britain is woven into the fabric of the European Union by countless threads of business, law, administration and security. Those strands cannot all be cut in a single slice: Some are desirable, even to the most committed Brexiteer. Ms. May will be judged on the extent to which she and her negotiators — led by the new Brexit secretary, David Davis — can repatriate control of immigration but retain access to the union’s single market.
This is a diplomatic conundrum of horrendous difficulty. It will test Ms. May’s new government to the limit.
The new prime minister must still deal with all the problems that exercised her predecessor. Her effective majority in Parliament of just 16 makes her vulnerable to legislative ambush in the House of Commons by Tory backbenchers. Back in the 1990s, such attritional warfare destroyed another Conservative prime minister, John Major.
The parlous state of public finances should ensure that Ms. May’s new chancellor of the Exchequer, Philip Hammond, will not want the government to spend more than it already does — though we do not yet know whether he is as committed to deficit reduction as his predecessor was. His priority will be to maintain a fiscal regime that encourages foreign investment in Britain and compensates for the chilling effect of Brexit on the economy.
Prime Minister May is neither a demagogue nor a showboater. As a senior minister, she was widely regarded as a technocrat, a practical politician rather than an ideologue. Yet her speech when she arrived in Downing Street was an exhilarating pledge to represent the disadvantaged, the excluded and those who, as she put it, are “just managing.”
It is precisely these voters who have felt most deserted by the political establishment and most detached from the Westminster soap opera. Ms. May’s outstretched hand is a bold gesture. It could end in angry disappointment, but what is the point of holding office if not to try?