When, decades from now, the history of these times is written, February 18 2019 will deserve a chapter on its own.

It was a day that shamed the Labour Party — and a profoundly worrying day for every British Jew. Because, on that day, a female Jewish MP reached the conclusion that the scale of antisemitic abuse she was receiving from Labour Party members and the deliberate, calculated and wilful refusal of the leadership to protect her from it, meant she could no longer remain in the party.

On Monday, in other words, a Jewish parliamentarian was, as Labour’s Deputy Leader Tom Watson put it, driven out of the Labour Party by antisemitic bullying — with the party siding not with her but with her abusers.

It is a devastating indictment of the Labour Party.

Heroism is a rare quality in politics. But the word is entirely appropriate for Luciana Berger. The MP for Wavertree has spent years as the target of vicious, foul abuse — and death threats. Six people have criminal convictions over such behaviour. But Ms Berger has never been cowed. She has fought both the abuse and those in her party who have refused to act against the abusers.

She was joined in leaving by Joan Ryan on Tuesday. Ms Ryan’s heroism is different but no less notable.

Some might say that, since she is not Jewish, this need not be her fight. But, as a woman of decency and principle, she has stood shoulder to shoulder with those who fight bigotry, and that stance has meant that she, too, has had to leave a party that has been, as she described it in her resignation statement, infected with anti-Jewish racism.

We salute — and thank — them both.

But, important as their stand is, and that of the other six MPs who have left Labour, the worrying truth that led to their departure is that Labour will not change.

The supposed fight to save it cannot be won. Those who now run the Labour Party are incapable of changing because antisemitism is in their political DNA.

Among Mr Corbyn and his allies, Israel is the greatest evil on earth. And because Jews are held responsible for Israel, we are seen not as the victims of racism but its perpetrators. So, for the Corbynites, the fight against antisemitism is not their fight — indeed, the antisemites are their allies.

That is why describing Labour as indecent barely comes close. Labelling it as institutionally antisemitic is merely a statement of the obvious. Labour is now rancid, with a leadership that considers its Jewish members — indeed the Jewish community itself — as expendable. As Joan Ryan puts it in her article inside, Labour now poses an existential threat to our community.

These are awful times. An antisemitic party, led by an antisemite, many of whose closest allies are antisemitic, is the official opposition.

Which is why attention must now focus on those decent MPs who remain in Labour. By staying, they are buoying up the most powerfully vicious, racist party Britain has ever known.

Every day they remain in the Labour Party, they themselves become more complicit in its antisemitism.