A row in Britain's main opposition Labor party over whether to back air strikes in Syria has deepened splits over Jeremy Corbyn's leadership, while reviving uncomfortable memories of wars in Iraq and Afghanistan.
Prime Minister David Cameron is expected to call a vote in parliament this week on joining the international coalition targeting Islamic State (ISIS) jihadists, but needs support from some Labor MPs to secure a majority.
The problem is that Corbyn - a left-winger who helped found prominent protest movement Stop The War Coalition - opposes air strikes, while many of his MPs support the move.
As well as complicating Cameron's calculations on whether he can win the vote, the situation has unleashed a round of very public feuding between pro and anti-Corbyn MPs about whether he is the right man to lead the main opposition party.
It is no coincidence that the row is about military action, the most sensitive issue for Labor since former leader Tony Blair led Britain into supporting the US in Iraq. The wars in Iraq and Afghanistan are now deeply unpopular in Britain, which lost over 600 troops.
"The Iraq factor is massive - it's front and center" for Labor MPs deciding whether to support action in Syria, according to Victoria Honeyman, an expert on British foreign policy at Leeds University.
"They're worried that they will look like they're following the Blairite approach to war, which is tainted," she added.
This is partly why Cameron spent several hours taking questions from MPs Thursday as he sought to reassure them that military action would be accompanied by a major push to find a diplomatic solution to Syria's four-year civil war.
"Trots in the bunker"
The key question facing Corbyn is whether he will let Labor MPs vote with their consciences or impose a "three-line whip" - a way to try and force the whole party to vote against air strikes, with consequences for those who do not.
This is expected to be decided at a meeting Monday, which promised to be explosive after he told the BBC on Sunday that he had the ultimate power to decide.
One of his closest allies, finance spokesman John McDonnell, supports a free vote but analysts say offering this could leave Corbyn looking like he cannot control his own party.
The leader himself has already written to Labor MPs saying he cannot support air strikes and emailed Labor supporters urging them to submit their views online, saying Sunday he had received 70,000 responses.
"Labor MPs need to listen to that voice," he said Sunday.
This has sparked fury among some, who accuse him of underhanded tactics by rallying support for his own position instead of waiting for the party to make a collective decision.
"How does Jeremy Corbyn and his small group of tiny Trots in the bunker think they've got the unique view on it all?" senior Labor MP John Spellar fumed on BBC radio Friday. "If anyone should resign after this incident, it should be Jeremy Corbyn."
Another Labor lawmaker, Paul Flynn, told the BBC there were "terrible divisions" while a third, Fiona Mactaggart, called Corbyn's position "unsustainable."
Democracy or division
Key to the row is the fact that Corbyn - a political outsider and serial rebel before becoming leader - was elected in September thanks to grassroots left-wing support, but is not widely backed by generally more centrist Labor MPs.
A YouGov/Times poll last week found that 66% of those eligible to vote in Labor's leadership election thought he was doing a good job - more than the figure who voted for him.
However, Labor is well behind the Conservatives in overall opinion polls.
If Corbyn does impose a three-line whip and try to make Labor MPs vote against air strikes, Honeyman predicted that some of his frontbench team could quit.
"If you're a member of the shadow cabinet and you defy a three-line whip, there's an expectation that your resignation will be on the desk in the morning," she said.
While that would be deeply embarrassing for Corbyn, it is not clear it would herald the end of his leadership.
The process for removing a Labor leader is complex and Corbyn has a huge mandate from activists, making any challenge to him problematic.
"I'm not going anywhere," the leader said Sunday.
Supporters insist nothing is wrong - in public at least.
"On Syria, can everyone calm down. We're all simply working through the issues and coming to final decision. Don't mistake democracy for division," McDonnell wrote on Twitter Friday.
AFP contributed to this report.