The accusation made here is that the election of Jeremy Corbyn created a toxic environment that has radicalised members of the party and this led to a growth of antisemitism in the UK. There is no need to overthink this. We know that Corbyn comes from a faction that has existed for decades on the fringes of the party. There is ample evidence that *some* of the new membership that joined to support him was antisemitic and extremist. These people were not ‘outsiders’ who ‘infiltrated’, but elements of the leaders own faction who joined to support the new leader.