Is our Corbyn strategy working?

Incident two. In the middle of a debate about the future of Labour with a non Jewish writer on Twitter, his interlocutor, a Corbyn backer, without warning suddenly asked the writer if he was paid by Israel. He said he was only asking, too.

Antisemitism will not go away if Owen Smith wins

Incident three. When Owen Smith claimed that antisemitism had become a problem on the left, the Corbyn supporting part of the audience jeered. This happens now whenever anyone raises the question of Jew hatred on the left. It is immediately rejected, portrayed as a baseless partisan attack on innocent people for political purpose.

We are, I'm afraid, losing the battle. Conspiracy theories about Israel and thus about Jews have become a natural part of left discourse. And while our attempt to alert people to the problem has had some success, the problem is still growing.

We have terrific, robust communal organisations and some of the people involved are the best in the business. They are also strategically savvy.

So what could the rest off us be doing differently?

Let's start here. The problem wasn't created entirely by Jeremy Corbyn. He may have made things worse, but it didn't start with him. For years, anti-Israel feeling has been growing on the left and it has slowly been changing into an antisemitic theory about Zionism as the ideology of worldwide imperialist occupation. By this means, every act of Western foreign policy has been linked to Israel and to Jews.

Just as the problem wasn't caused by Mr Corbyn, so I fear it will not go away if he loses the leadership.

It is just about possible that Mr Smith will win. If he did, does anyone think the antisemitism problem would go away? I certainly don't. In fact were Mr Corbyn to be deposed I fear that a part of his support would blame the Zionists. Us, in other words.

This provides us with two strategic alternatives. The first is to continue to pin the blame for the rise of antisemitism on Mr Corbyn. We attack his miserable failure to counter the problem, we make clear how his associations have made the problem worse, we draw attention to the Corbynite allegiance of those making antisemitic comments on social media.

This tells the truth, raises the profile of the issue and ensures that those on the left who do not support Mr Corbyn are made aware of the problem and become more determined to tackle it.

This broadly is what we have been doing and there is a lot to be said for it. But it has drawbacks.

As any social psychologist will tell you, this approach also solidifies some Corbyn supporters in their antisemitism. It makes anti-Zionist conspiracy theories part of the group identity of the left.

You can see it happen. Mr Corbyn numbers among his fans the strongest opponents of racism. Yet these very same people jeer when obvious examples of antisemitism are raised. They cannot accept that there is antisemitism because to do so is to accept criticism of themselves.

So an alternative strategy is to isolate people who make antisemitic comments and argue that they are letting down the Corbyn side.

This would involve accepting the leader's protestations that the problem is nothing to do with him and decoupling the idea of antisemitism from its association with Corbynism.

This might well be more effective. At the same time, it is less obviously true, might be weak and will mean that the solid support we have been receiving from the other side of the Labour party might wane in enthusiasm.

Do you see what I mean about asking a question and not being entirely sure of the answer?

Daniel Finkelstein is associate editor of the Times