Former Prime Minister Tony Blair responds to questions from journalists on the final day of the 2002 Labour Party Conference in Blackpool.Phil Noble / Reuters

MANCHESTER, England—My first party conference was Labour’s, in Blackpool, 2002. Tony Blair was at his zenith, Bill Clinton was the star guest, and Kevin Spacey, accompanying the former U.S. president to England’s depressed northwestern coast, was still a Hollywood celebrity who made politicians look good.

I was there to see Blair. Eighteen at the time, I’d never truly been aware of another prime minister. When I was growing up in a Labour family in Blair’s constituency, Sedgefield, in the northeast of England, he was an ever present figure in my life, before he became one in the country’s.

Back then, he seemed to be the image of a modern prime minister—a prototype that others had to follow. There was something prophetic in his sermon (a mortal weakness few spotted at the time): His way, progressive centrism, was the only way to do politics. Blair proved his own theory in Britain, as Clinton had in the United States. “Here we are in this interdependent world of open borders, easy travel, mass migration, universal access to information and technology, drenched in global media,” Clinton told the crowd before offering a “stunning” example of how the world was changing: A friend had called him on a cellphone to say he’d seen him arriving in Blackpool on a television in Paris. Such a scene now seems almost touchingly quaint.

As I look back, here at the Conservative Party conference in Manchester, it’s as if 2002 is from another era entirely—like one of those viral Ronald Reagan clips hailing the positive impact of immigration. Seventeen years ago, Blair was king—fresh from a second landslide victory, all-powerful, and on a mission, six months before ensnaring himself in Iraq.

The Blair and Clinton rule book was simple. Successful political leaders were a sacrifice party activists had to endure for their side to win power. Real leaders defined themselves against their party’s instincts and used conferences like the one in Blackpool to talk not to their base, but to the country at large. Politics was a consumer industry, and political parties were businesses, not charitable cooperatives run by the workers.

For the first time since I started attending these strangely British political jamborees, the rules of the game as laid out by Blair have been entirely junked. Britain’s political leaders are now tribunes of the party base, amplifying their demands, not challenging them. Jeremy Corbyn has played this role ever since ascending to the Labour throne in 2015. He is the activists’ hero, defining himself against Labour’s members of Parliament, not the party’s base.

What is unique about 2019 is that this now applies to both main political leaders. In Manchester, Boris Johnson has been cheered everywhere as the conquering Tory hero, a kind of Brexit Corbyn. After the drab, depressing years of Theresa May and the insults toward the party from David Cameron, here is a true Tory. The “mad, swivel-eyed loons” are now doing things their way. Enough of the sacrifice.

The break with the recent past signals a fundamental shift in British politics following the 2016 Brexit referendum. Gone are the attempts to establish a compromise position acceptable to the center. In the Brexit civil war, there is no “third way” between Remain and Leave—you must choose a side.

In Blair’s Britain, political leaders were modern, centrist, progressive. He had taken on the left in his party and won, symbolically stripping out the old “clause four” of the party’s constitution that promised to socialize the economy and replacing it with mushy aspiration. After being elected prime minister, he promised not to turn back left, vowing that he had campaigned as “New Labour” and would govern as New Labour. His failure to challenge the Thatcherite economic consensus is held against him by the left. To be called a Blairite within Labour today is a pejorative.

After Blair, Gordon Brown came and went, unsure whether to distance himself from his predecessor or copy him, speaking of Real Labour (not New Labour) one minute, only to invite Margaret Thatcher to 10 Downing Street the next. Cameron, the heir to Blair, soon saw him off, selling the Conservative Party with a familiar image—a modern man challenging his party.

In 2009, a year before becoming prime minister, Cameron declared there was “such a thing as society”—a symbolic yet direct rebuke to Thatcher’s infamous remark that there was not (the rest of the sentence reads: “There are individual men and women and there are families. And no government can do anything except through people, and people must look after themselves first. It is our duty to look after ourselves and then, also, to look after our neighbours”). In 2011, he challenged the party to back gay marriage, telling activists he did not support the move “despite being a Conservative, [but] because I’m a Conservative.” It was a move straight from the Blair playbook.

Even May stuck with the Blair strategy, challenging her party to temper its instincts to attract voters on the other side, and adopting some of the interventionist economics of the Labour opposition.

Judging by this year’s party conferences, this model has now all but disappeared. Johnson and Corbyn are in power because the party’s grass roots put them there; they were elected on a platform that they did not have to compromise on to win and keep power, at least within their parties.

The irony is that Blair is one of the leading protagonists in the latest fight over Brexit, urging those who voted to Leave not to give up on Britain’s membership of the EU and instead push for a second referendum to overturn the first. Johnson and the Brexit ultras in the Conservative Party in turn argue that any Brexit is better than no Brexit, deal or no deal.

The seeds of this culture war can be seen in Blair’s 2002 address to his party in Blackpool. Here are the two sides of Blair: the conservative and the radical prophet. He warned his party members that they must go to places they find uncomfortable by reforming schools and hospitals, not only increasing their resources. The country needed to be bold, he said. “I believe we’re at our best when at our boldest.” That meant reform at home, activism in Europe, and intervention in the wider world—including in Iraq if Saddam Hussein did not come to heel. This Britain has almost vanished: Whereas Blair said adopting the euro currency was part of the country’s “destiny,” Britons instead opted to leave the EU entirely; military adventurism overseas is now on life support after Cameron’s 2013 failure to win parliamentary authorization for air strikes against Syria.

Blairism is as dead as the rules he established for winning power. The next election will be won not from the center, but by the party that can get out its vote—more Karl Rove than Bill Clinton.

Still, even here, the followers of the prophet Blair will see a warning from his political grave. “Never let us fall for the far left’s eternal delusion,” Blair warned in his 2002 speech. “That if there is dissatisfaction with a moderate center-left government, this can be manipulated into support for a far-left government. It results only in one thing. Always has. Always will: the return of a right-wing Tory government.”

British politics is testing Blair’s theory to destruction.

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