Before Mr Corbyn became Labour leader it would have been inconceivable to have felt any need to ask Jewish voters whether antisemitism is an important factor in deciding how they would vote.
But today, because Labour is led by an antisemite and is regarded as institutionally antisemitic, not only is the question vital, 96 per cent of British Jews say that it is indeed important.
This is where Brexit comes in. Such is the political chaos that an election is far from impossible, with the possibility — likelihood, even — of a Labour government following, with an antisemitic Prime Minister buttressed by an institutionally antisemitic party. Which is why all decent Labour MPs must now — not at some indeterminate date in the future, but now — decide if they can remain.
While they stay, they are the enablers of antisemitism. If they cannot have that on their conscience, they know what they must do.