Anyone who’s ever had a conversation with a Corbynista will know it’s impossible to talk to these people about anti-Semitism. The minute you mention the world’s oldest hatred their ‘buts’ come flying. ‘But what about Islamophobia?’, they say. ‘But what about other forms of racism?’, they cry. It’s like a tic, an involuntary ideological spasm that makes them mouth that intrusive ‘BUT’ before you’ve even got through all six syllables of ‘anti-Semitism’.