<sod >Shadow chancellor John McDonnell has told supporters that it would be âreally toughâ for Jeremy Corbyn do as well as he did in 2014 â but insisted it would not weaken his mandate.< eod>< sod > Shadow chancellor John McDonnell has told supporters that it would be âreally toughâ for Jeremy Corbyn do as well as he did in 2015 â but warned critics it would notÂ dilute his authority.< eod>