How quickly a mood can change and a different atmosphere can take hold.

In the days leading up to Pesach, British Jews and their allies stood shoulder-to-shoulder in Parliament Square, protesting against Jeremy Corbyn’s inaction on tackling antisemitism in the Labour Party. 

MPs took notice. The national media took notice. It felt as though, after two-and-a-half years of whistling into the wind, the country was finally taking notice.

Here we are, a fortnight later, and what have we got? Mr Corbyn emboldened by supporters who rally around him — rather than against him — and our own community doing a reasonable impression of acting like ferrets in a sack, engaged in petty squabbling among ourselves.

One of the great strengths of the activity around the Board of Deputies and Jewish Leadership Council “Enough is Enough” initiative to hold Mr Corbyn to account last month was the sense that it was a spontaneous cross-communal surge of feeling. 

Since then, we have gone backwards. The appearance of the Labour leader at a Jewdas Seder last week was, for him, a rare strategic masterstroke; it immediately set British Jews against one another. 

To see the Board of Deputies’ president on national television calling other Jews antisemites must have been as thrilling for Mr Corbyn as it was shocking for the rest of us. 

Next consider the Campaign Against Antisemitism demonstration outside Labour’s headquarters on Sunday. 

Well-intentioned it might have been, but the event quickly became the scene of pantomime booing of the Jewish media and criticism of prominent figures and invited speakers.

David Abrahams, until recently a major Labour donor, was attacked for suggesting the community might want to consider how it will continue dialogue with Labour in the future.

He was booed and subjected to chants of “off, off, off!” as though he were a lower league footballer who had mis-timed a clumsy tackle, rather than a multi-millionaire with a nuanced outlook on dealing with a political party.

The aftermath of the event focused on that most interminable of post-rally regularities — a row over the number of attendees. This is what we are now reduced to: “Look how big our crowd was!”, “No, we’re the toughest on tackling Jew-hate!”, “Our placards have the nicest font!”. 

If British Jews cannot be on the same side in tackling antisemitism, what hope is there? 

The hard-left thrives on splinter groups going head-to-head, internecine rivalries that baffle normal, mainstream people and hamper those involved, stopping them from holding the government to account, or indeed planning for a Labour government to lead the nation.

Mr Corbyn and his supporters have, in relatively short order, succeeded in halting the momentum that was building against him on antisemitism and, it seems, fracturing the resolve of the Jewish community.

Good Jews versus Bad Jews. Red Jews versus Blue Jews. True Jews versus Fake Jews. 

What a mess — and how Mr Corbyn and his band of deluded conspiracy theorist allies must be chuckling to themselves.