Such a clear U-turn would cement a corrosive narrative that could prove far more damaging to his prospects of becoming Prime Minister – that of weakness.
The country's voters show little desire to proactively seek a resolution to the euro crisis.
The former election co-ordinator's call for an early EU referendum highlights the danger of Labour replicating Tory divisions over Europe.
A Conservative majority remains unlikely and EU treaty change could take many years to come to fruition.
With Scottish voters far more pro-European than their English counterparts, the increasing doubt over EU membership could shift the odds in favour of independence.
The six Labour MPs who voted in favour of Tory MP James Wharton's EU referendum bill.
Shadow minister Ian Austin's dramatic call for an in/out referendum next year shows how party unity is fraying.
Both pro-EU, both queasy about a referendum. Who will jump first?
Withdrawal from the European arrest warrant would turn the UK into a haven for foreign criminals.