When Zack Polanski addressed his campaigners flush with victory after the Gorton and Denton byelection in February, he declared: “Labour’s electoral stranglehold is over.” The election of Hannah Spencer as the new Green MP for the Greater Manchester seat was a seismic victory, he continued: “I said we were here to replace Labour and this is what replacing looks like.”But in the wake of Polanski’s defeat in the Holborn and St Pancras byelection on Thursday, and a calamitous row over the party’s stance on Zionism, the debate around what, or who, could be replaced has shifted to Polanski himself.On Friday...