How did we get into this situation? Last week we were faced with a choice. Theresa May offered a strong and stable Brexit and the electorate just laughed at her. They didn’t want it implemented; that was last year’s cry of resentment. This year’s was Jeremy Corbyn.

And why is he the only alternative? If you don’t know by now that Mr Corbyn embraces certain kinds of antisemitic and totalitarian politics, then you don’t want to know.

I thought that Mr Corbyn’s work for the Iranian propaganda TV station alone disqualified him from leadership; or the fact that he had once said that Hamas and Hezbollah were dedicated to peace and justice; or that he supported a boycott of Israel but nowhere else on the planet.

But we need to stop being surprised. I was shocked when my academic colleagues voted to boycott Israel; and again when they failed to understand why that was so wrong; and again when we were pushed out of the discussion in the University and College Union; and when the Employment Tribunal listened to our evidence about antisemitism for three weeks and then told us it all amounted to a dirty trick to silence criticism of Israel; and again when Mr Corbyn was elected leader; and then a second time; and when Shami Chakrabarti whitewashed the Labour Party inquiry into antisemitism; and then when Mr Corbyn came within a sniff of No 10.

It turned out that there were only four constituencies where Labour was punished for its leader’s antisemitism; all four are home to significant Jewish populations. Those four Labour gains from the Tories might have made a difference. Antisemitism did not seem to be an issue anywhere else.

We don’t know if people just don’t care about antisemitism; or if they don’t know; or they don’t want to know; or they don’t understand; or they think it’s all a Zionist and Tory smear; or if they just think Mr Corbyn wants to help Palestinians; or if they judge him to be an antisemite but vote for him anyway, because there are other issues in the mix, too.

But Mr Corbyn is also a cypher, a blank populist canvas on to which everybody paints their own fantasy.

Lots of Ukip supporters in the old Labour heartlands voted for him. London Remainers voted for him. People who hate the cash squeeze on the NHS voted for him. People who don’t want to help pay for their children to go to university voted for him. People who work hard but can’t afford somewhere to live voted for him.

People who blame British foreign policy for terrorism and people who imagine that if we were nicer, the terrorists would leave us alone voted for Mr Corbyn. People who admire Hamas, the IRA, Hezbollah, Chavez, Castro and Putin voted for him. People who blame bankers, the Rothchilds and the “Davosocracy” voted for him. People who like his refusal to step into line voted for him. People who hate him but like Labour voted for him. People who hate Labour but like him voted for him.

We’re going to be in an impossible position in the next election. I don’t know how we’re going to get out of it but I know how we got into it. We were unable to stop antisemitic politics being normalised on the left and we were unable to stop it from moving into the mainstream. And liberal Tories were unable to stop the politics of resentment and xenophobia from mainstreaming, too.

Tories need to understand that denouncing Labour voters as Nazis is not a strategy; they have to understand how their own populism endangers British democracy. As Michael Heseltine said, if they press ahead with Brexit now, they will give us Jeremy Corbyn as Prime Minister. They need to offer an alternative to Mr Corbyn, not a mirror image. Promising to tear down European co-operation and institutions and to license the rise of xenophobic nationalism will not pull middle-England away from the small marginal swing to Labour that would give us a Corbyn government.

And we on the left have to start winning our basic arguments. We have to force Corbyn to account for his past if he is to carry on into future; we have to keep our courage and not go silent; we must not be seduced into acquiescence by a sniff of power. We will not stop educating people to recognise and oppose antisemitism; we will not stop calling it out when we see it.

Antisemitism is not one little eccentricity; it is an indicator of a profound political malaise. It cannot be ignored.

David Hirsh is a sociology lecturer at Goldsmiths, University of London and author of ‘Contemporary Left Antisemitism’