Last week was Jeremy Corbyn’s worst week ever as leader of the Labour Party—that was until this week.

A widely-shared blog today from Conservative journalist Chris Deerin spares no sympathy in its utter dismissal of Jeremy Corbyn as a serious political figure in British politics. “The Corbyn leadership is the most farcical, ill-advised and embarrassing episode in British political history. Everything about it is wrong. And, as I say, it is already over.”

There are Corbyn supporters who will dismiss these words as a howl of fear from a frightened establishment figure. But for many MPs and moderate members, Deerin is simply voicing what they always feared would happen under Corbyn, and now believe, with sadness and unbearable frustration, to be true.

But it’s not just about the future of Jeremy Corbyn that’s at stake anymore, according to Dan Hodges, who wrote a piece today where he argued that the threat to the party’s survival is now urgent and existential. “Now it is about the Labour Party – and a week that could come to define the Labour Party.”

This is the week the Prime Minister will put the case to Parliament for airstrikes against Islamic State in Syria, and there can be no more “open debate,” as Corbyn has favoured on difficult issues till now, about what the Labour position will be. Labour must come to a decision, as a party, and Corbyn cannot hedge with a free vote, allowing his front bench to veer off in different directions. As Jonathan Todd writes on Labour Uncut: “It’s time to take a stand.”

“There have been times in our nation’s history,” Hodges writes, “when our political parties have adopted the right stance on military intervention. There have been times when they have adopted the wrong stance. But I cannot recall an occasion in my lifetime when one of those parties failed to adopt any stance at all.”

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But it was last week, until this week, that was Corbyn’s worst week ever.

Pressure has been building in the party since August, as a reemergent far left, emboldened by a huge intake of new Corbyn-supporting members, has clashed with with the Parliamentary Labour Party, which remains largely moderate.

Corbyn’s enormous victory in the leadership election seemed to cement his mandate for at least the next two years, if not until 2020. But the left has struggled to assert its control and dilute internecine strife.

Some moderates have employed a strategy of allying with the left of the party to make it work. Though Monday meetings of the PLP have been consistently hostile and confrontational, though many MPs have regularly briefed against the leader, and though some MPs have gone as far as to openly condemn Corbyn on an almost daily basis, there has been an unspoken rule up until now that, given Corbyn’s mandate, the centre and right of the party must accept its moment is now over, and, until Corbyn’s leadership can be tested in upcoming elections, allow the left to steer the direction of the party.

But with rumours of a coup tonight, the “make it work” days seem have come to an abrupt, and remarkably quick, end. That’s largely to do with what played out last week, starting with what many saw as Corbyn’s poor response to the terrorist attacks in Paris.

Last Monday, at a meeting of the PLP, the feeling in the party suddenly shifted. Corbyn was shouted down by some of his own MPs during a fiery argument about comments he gave during a BBC interview where he appeared to question a police ‘shoot to kill’ policy in the case of a Paris-style attack in the UK. After the meeting, one of Corbyn’s front benchers branded the leader a “fucking disgrace”.

But the week got worse for Corbyn on Wednesday when MPs lashed out over his surprise announcement that Ken Livingstone, a trusted friend and anti-Nuke ally on the far left, would co-chair the party’s defence review. Shadow defense secretary, Maria Eagle, who had been leading on the review, said she was not consulted before the appointment.

Things continued to deteriorate. When shadow defence minister Kevan Jones, who has suffered from depression in the past, questioned whether Livingstone had any defense experience, Livingstone responded by saying Jones was “obviously very depressed and disturbed” and “should see a GP”. Corbyn, who has promised a new era of nicer, kinder politics, asked Livingstone to apologise, which he initially refused to do before offering one on Twitter. There were no further repercussions from Corbyn’s office.

But it got worse. On Saturday, Corbyn gave a speech calling for a new kind of foreign policy that gave the UK a “more independent” relationship from the rest of the world where “war is a last resort”. The speech coincided with the announcement that the UN Security Council had unanimously approved ‘all necessary measures’ against Isil in Syria. Responding to the announcement, Prime Minister David Cameron said, “We cannot expect others to shoulder burdens and risks of protecting this country”. Many Labour MPs have lined up to back up the Prime Minister’s call for action.

Labour MPs have sought to distance themselves from Corbyn’s anti-interventionist approach to foreign policy. Chuka Umunna, a former candidate for the Labour leadership, told the Today programme: “The first duty of any elected representative, not just ministers, is to do all we can to ensure the security of our constituents, particularly in the face of the terrorist threat we are facing.

“This goes above and beyond party politics, and dare I say it internal party politics. Because if you cannot keep the people safe in their eyes, that is a disqualification from office.”

Then on Saturday evening a ComRes poll for The Independent on Sunday was published showing that a 15 point gap had emerged between Labour and the Conservatives. NumbrCrunchrPolitics tweeted that at 27%, compared to the Conservatives’ 42%, this was Labour’s worst poll while in opposition since September 1983.

That was last week. This week will be the true test of Corbyn’s ability to handle and fight off his opponents in the Parliamentary Labour Party. Anger and defiance on the right of the party is growing, but, as the Times reports tonight, an exclusive poll shows that Corbyn remains the overwhelming first choice for the Labour grassroots, with 66% of members backing him. It’s likely to be a bad week again for the Labour party.