Many of Jeremy Corbyn’s supporters are incredulous that a party he leads could be accused of having a problem with anti-Semitism. “He’s a life-long anti-racist”, they protest.

Corbyn showed some of this passionate opposition to racism when he forced out his Shadow Secretary of State for Women and Equalities, Sarah Champion, for comments about the relationship of some Pakistani men to grooming.

In an article in The Sun, Champion wrote: “Britain has a problem with British Pakistani men raping and exploiting white girls. There. I said it. Does that make me a racist?”

Speaking about Champion’s resignation, Corbyn said it was wrong to “label a whole community”.

People will have different views on whether Sarah Champion ought to have been ousted for what she wrote, but the Labour leader’s clarity of conviction was undeniable.

There was to be”zero-tolerance”of comments that disparaged the Pakistani community.

It is understandable that many in the Jewish community will be asking why this “lifelong anti-racist”, who has proven he can show real determination in confronting what he perceives as bigotry, cannot bring himself to act with similar force when the problem of Jew-hatred surfaces.

There was another opportunity to send a message on this last week when Shadow Fire Minister Chris Williamson used an interview with The Guardian to pour cold water on concerns that Labour had a problem with anit-Semitism, dismissing the series of scandals as “proxy wars and bull***t”.

This is the latest in a long line of senior Labour figures who should know better, failing to confront the problem and instead seeking to minimise and gloss over it.

In stark contrast to the robust response to Sarah Champion, there was not even a gentle rebuke from the leader’s office.

This despite this being Williamson’s second equalities-related imbroglio in just a week, having earlier backed a call for women-only carriages.

Part of the reason that Labour’s passivity on this issue hurts so much is not just that it is clearly morally wrong, but even on a cynical, tactical level it would be better to act with determination and put these problems behind the party, rather than letting them fester on.

So, why the double standard where some racisms are more equal than others?

It is increasingly clear that, for some sections of the left, whereas certain minorities can be pitied and patronised, the fact that Jews are often white and middle class affords us no such sympathy.

And in any case, the unthinking, trendy-left hatred of Israel seems to justify any abuse of Jews, even where comments have nothing to do with Israel, like bogus claims about Jews being “chief financiers of the slave trade”.

After a far stronger showing in the recent election than was expected, some around the leadership may feel that they have no need to act. Their problem is that history is a harsher mirror than any election.

In his heart, Jeremy Corbyn may well be a deeply committed anti-racist, but if he does nothing more to root out the anti-Semitism that festers in some parts of the left, his legacy will not be one of anti-racism. It will be one of inaction in the face of the world’s oldest hate.