For a long while I thought anti-Semitism was incidental to the extreme left in Labour.
I thought anti-Israel sentiments were a convenient peg on which to hang a general 'we are for the underdog' policy.
But over the last months I've come to realise that anti-Semitism is not incidental to the thinking of the extreme left in Labour at all.
Rather, it's part of the extreme Left's understanding of world history, of the political classes, of the class struggle. Jeremy Corbyn cannot 'fix' antisemitism in the Party because he sees the march of world history this way, too.
The evil, grasping exploiting Jew is a real figure in his and their understanding of how the world works.
Even when it is pointed out to them that the world is full of exploiting people who are not Jews, they believe there are bigger more villainous Jews behind them, secret groups who pull the strings.
It's religious, really, the belief in this hidden hand that controls world history and that they are the saviour of the downtrodden masses.
How can one decide whether this description of the hidden hand of world history is true or a delusion? Really there is no way, because the 'hidden hand' is by its nature hidden. And that is so convenient for them, so convenient to have a hidden foe.