J.K. Rowling is in a massive Twitter war about the future of progressive politics in Britain

For roughly a day now, Harry Potter author J.K. Rowling has been in a bitter fight with her Twitter followers. The row has nothing to do with wands or Dumbledore’s sexuality. It’s all about UK politics — and it sheds a lot of light on what’s happening in that country.

Rowling, in case you aren’t familiar with her politics, is one of the UK’s most famous progressive voices. She’s a passionate believer in expanding the welfare state — she wrote the first Harry Potter book whilst a single mother on welfare — and was an outspoken opponent of Britain’s vote to leave the European Union.

But Rowling isn’t fighting with Conservatives this time. Instead, she’s attacking Jeremy Corbyn, the left-wing firebrand who has led the UK’s Labour Party. Rowling, a longtime Labour supporter, is furious with Corbyn’s leadership:

To understand why, you need to understand a little about Jeremy Corbyn.

Corbyn is a socialist — the real thing, not like Bernie Sanders. The BBC has an excellent rundown of his policy platform, which includes, among other things, renationalizing Britain's railroad system and energy companies, abolishing tuition for British universities, and imposing rent controls to deal with Britain's affordable housing problem. He's even open to reopening the coal mines that used to be a big part of Britain's economy.

In the 1980s, the last time Labour stood for this sort of thing, it was repeatedly trounced by Conservatives. Two Labour Party leaders — Tony Blair and Gordon Brown — blamed their party's left-wing platform for its losses, and became the leaders of a movement called New Labour. Think of it like a British equivalent of Bill Clinton and the Democratic Leadership Council: a force that pulled the party to the political center, particularly on economic issues, in the name of electability.

New Labour initially succeeded. It took over the party in 1994, when Blair was elected leader, and controlled the premiership from 1997 to 2010. But in 2010, the brand was retired after the Great Recession led to electoral defeat.

However, New Labour's ideological influence is far from gone: Labour's mainstream and its leadership is still far more free market-oriented than it was in 1983, the year a landslide electoral defeat began the shift toward New Labour. So Jeremy Corbyn’s victory in the September 2015 party leadership election was a complete and total shock.

Since then, he has faced a number of rebellions from the Labour upper ranks. He’s currently in the midst of a primary challenge, from Labour MP Owen Smith.

But Corbyn has fended off all of these challenges — the majority of Labour voters seem fed up with the more liberal-than-leftist approach of New Labour, and support Corbyn’s more unapologetic socialism. The most recent YouGov poll shows Corbyn beating Smith by a whopping 62-38 margin.

And yet, Labour has collapsed among the general UK election. Britain Elects, a UK poll aggregator, shows Labour support collapsing in recent months:

This is what Rowling is so angry about. It’s not so much that she disagrees with Corbyn’s policies, at least openly. It’s that she, and a number of British liberals, believe that Corbyn’s hard-line leftism will doom Labour to political irrelevance and the UK to Conservative government. While the Corbynites see New Labour as sellouts, Rowling and her ilk see them as a better alternative to the Tories. Where the Corbynites see a political revolution, Rowling sees a rerun of the 1980s.

If you look at Rowling’s feed right now, she’s still retweeting followers and fighting with them about Corbyn.

Her tweets point to the huge stakes in the Labour fight. For Rowling, the stakes are nothing less than the survival of the UK’s center-left party and the maintenance of the welfare state. For Corbyn supporters, the stakes are the viability of an unapologetic leftism in modern Britain, and the defeat of a form of center-left liberalism that they see as bankrupt and essentially conservative.

That’s why the internal fight in the UK Labour Party right now is so passionate — and so important. It’s a debate over the future of the political left writ large: Of whether a return to old-school socialism is both desirable and politically possible. Liberals and leftists around the developed world are watching.