Such is the frequency of revelations about Jeremy Corbyn that it sometimes feels as if you dare not blink lest you miss something.

Whether it is a picture of him laying a wreath to honour terrorists, the latest discovery of him speaking alongside people who wish to see as many dead Jews as possible or a recording of words he has uttered at such a meeting, the evidence — known in Corbyn-speak as a ‘smear’ — is voluminous.

But last week’s video recording of the Labour leader’s curt reference to Zionists who “don’t understand English irony” was of a different order of magnitude. Until now, his defenders have tried to argue that he is, in effect, what Dave Rich has described as the unluckiest anti-racist of all time — a man who just happens to end up sharing platforms with antisemites.

Even that is no longer tenable.

From his own lips we hear a version of classic English antisemitism — the idea of the Jew as alien, not really fitting in with what it means to be English. His acolytes have, of course, attempted to spin this away but such attempts fool no one.

It is now impossible not to regard Mr Corbyn as an antisemite — and Lord Sacks is quite right to speak so plainly. 

In this context, it has been revealing to see the extent to which the Corbynites are now attempting to blacken Lord Sacks’s name, such as labelling him as a “far-right extremist”.

Their strategy is clear: they are attempting to deligitimise Jewish criticism  of Mr Corbyn on the basis that it supposedly comes from right wing, nationalist Trump types and as such is politically motivated and can be dismissed.

This is not so much distasteful as dangerous. But it is how they operate, and we must be prepared for the fact that worse is likely to come.