This will have been a bitter discovery for Jeremy Corbyn’s supporters – the young people he brought into the Labour Party had most to lose from Brexit and were those most passionately in support of staying in the European Union.
Their sense of betrayal is huge and was understood by Corbyn’s office – they stood him down from a planned appearance at Glastonbury.
That was wise – his speech would have had a reception worthy of the old Glasgow Empire music hall, whose unofficial motto was “no turn left unstoned”.
But it was telling too. This is a moment of weakness for Jeremy Corbyn – he is wounded, will the Parliamentary Labour Party move in for the kill?
Of course, in one sense they have to. If you do not act after your leader loses one third of all remaining Labour voters to the Leave cause, then when will you?
Remember, the Labour Party and the entire labour movement have strongly supported the EU for nearly 30 years.
While there have been doubts about whether they had the stomach for a fight before now, there can be none now.
The shadow cabinet have gone over the top in waves, starting with Hilary Benn who was sacked by Jeremy Corbyn after telling the leader that he did not have any faith that he could win an election.
It is this – the prospect of a snap election called by a new Tory prime minister chosen in the autumn – that has focused the minds of Labour MPs.
It is one thing to imagine a Labour defeat in far-off 2020, it’s quite another to see a rout coming in the autumn – a landslide in which you might very well be a pebble. As Dr Johnson observed: “Sir, when a man knows he is to be hanged in a fortnight, it concentrates his mind wonderfully.”
There are many reasons why Corbyn should go – his failure to lead on Brexit is just one of a long list that includes his lamentable PMQs performances and his shambolic shadow cabinet reshuffle.
But there is one main reason that he will be taken down as leader – it is in the self-interest of Labour MPs to move on him now.
Will this coup be successful? This is the best chance that plotters have – MPs are motivated and members have a genuine grievance over Europe.
Will it be easy? No. Revolutions are inevitably bloody and, make no mistake, taking back the Labour Party from Jeremy Corbyn and John McDonnell requires a revolution.
Who will be the new leader? Worry about that after the coup succeeds.
Labour has to sort its own house out before getting onto the serious business of holding the Tories and their new leadership to account for the disaster of Brexit.
John McTernan is a former adviser to ex-Prime Minister Tony Blair and political strategist