Jeremy Corbyn is under mounting pressure from his shadow cabinet to give Labour MPs a free vote on airstrikes against ISIS in Syria.
The party leader needs to decide whether to follow his heart and order his party into opposing military action – or follow his head and allow MPs to vote with their consciences.
One thing is clear – there's not a big appetite for resignations at the top of the party. BuzzFeed News understands that most shadow cabinet members are keen to make sure "sensible" voices stay in place.
One shadow cabinet minister believes it is "60% likely" that Corbyn – a long-time anti-war campaigner – will whip the vote, which is expected in the House of Commons as soon as Wednesday.
Corbyn has been bolstered by a Labour survey which found that 75% of respondents were opposed to bombing, with only 13% in favour. The party received 107,875 responses but only analysed a sample of 1,900.
Corbyn is likely to emphasise that not only is there strong opposition to airstrikes from party supporters and trade unions – but also from many Labour backbenchers who have not yet been convinced by David Cameron's arguments.
The scepticism among the parliamentary Labour party (PLP) weakens the position of many shadow cabinet members, including deputy leader Tom Watson and shadow foreign secretary Hilary Benn.
A source close to a shadow cabinet member said: "This is his [Corbyn's] life's work. If he thinks there's a chance he can singlehandedly stop Britain bombing Syria, he will take it. But the reality is, the bombing is still going on. We're already in Iraq. America, Russia, and France are already in Syria."
Shadow international development secretary Diane Abbott, a close ally of Corbyn, will be urging Corbyn to order his MPs to oppose airstrikes at the shadow cabinet meeting on Monday afternoon. It has been pushed back from 1pm to 2pm.
"Party members, and increasingly the country, want to see us oppose these airstrikes – which are not the solution – with every sinew of our being, and that would mean a three-line whip," Abbott told BBC Radio 4's Today programme.
But shadow chancellor John McDonnell, another close ally, believes MPs should get a free vote because it is "a matter of conscience".
A source close to another shadow cabinet member told BuzzFeed News Corbyn will probably come to a compromise on the Syria vote. They said he might whip the vote but suspend the principle of "collective responsibility", so that shadow cabinet members will not have to resign or be sacked.
"Most people will want to stop this being a big resignation issue because it doesn’t really get us very far," the source said. "There are lots of sensible people in the shadow cabinet at the moment. Those people need to stay."
There is anger among much of Corbyn's shadow cabinet that he published a letter outlining his own view on airstrikes on Friday, before they made a collective decision on Monday.
"It had been agreed there was a process – a meeting of the shadow cabinet on Friday and Monday and then a PLP meeting – but he broke their trust, he threw that out of the window and it's bollocks," the source said.
"He sent that letter to try and bounce MPs into coming round to his position. That’s not the new politics. It’s the same old hard-left tactics."
Corbyn insisted on BBC1's Andrew Marr Show on Sunday that it was his decision alone whether or not to whip the vote. But Labour's own rulebook suggests it's the shadow cabinet – not the leader that makes the final decision.