Now it's Keir Starmer's turn. After Boris's shock defeat in Chesham and Amersham, Labour is on course for another Red Wall by-election disaster, this time in Batley and Spen.
But while the Tories were victims of a combination of local factors, including opposition to HS2 and proposed planning reforms, Labour strategists have identified a single, toxic reason for their impending loss.
'We're haemorrhaging votes among Muslim voters,' one senior Labour official tells me, 'and the reason for that is what Keir has been doing on antisemitism. Nobody really wants to talk about it, but that's the main factor. He challenged Corbyn on it, and there's been a backlash among certain sections of the community.'
The direct beneficiary of that backlash is George Galloway. The former Labour and Respect Member of Parliament has brought his political circus – and trademark black fedora – to West Yorkshire.
And according to MPs and strategists I've spoken to from all parties, he's currently eating the Labour vote alive. 'I'm in the lead here,' he tells me in a disarmingly matter-of-fact way. 'I'm going to get around 13,000 to 14,000 votes. And in a by-election that should be enough. Labour are going to come third.'
The direct beneficiary of that backlash is George Galloway (pictured). The former Labour and Respect Member of Parliament has brought his political circus – and trademark black fedora – to West Yorkshire
The implication of Galloway's belated arrival in Batley was supposed to be clear. His ability to leverage votes from the Muslim community would erode Labour's support, allowing the Tories to slip through the middle. And it's true that he's hoovering up the Muslim vote. 'I'm hegemonic in Asian areas,' he tells me. 'It's the benefit of 50 years of work. Speaking out on Palestine and Iraq. Standing up for Muslims at home and abroad.'
Then last week, people began to notice a shift in his tactics. At the start of the campaign, Galloway was spending time exclusively in ethnic-minority areas. Now, he's targeting Labour's traditional white working-class support.
'The white working class despise Labour,' he tells me. 'They think Labour just don't like them.
'Things like the whole LGBTQI agenda. The working classes don't like that. They're tired of Labour's identity politics.'
Contrary to popular perception, Galloway's campaign is not a single issue pitch on the plight of the Palestinians, but a full-on assault on woke, metropolitan liberalism. He's unashamedly pro-Brexit. His 'residents' surveys' highlight crime and anti-social behaviour. He has lambasted those criticising fans for booing players taking a knee. Yet despite his slightly ironic pledge to 'build the new Jerusalem', there is a dark shadow hanging over Galloway's drive to deliver another body-blow to the British political establishment. Take his reference to LGBTQI issues.
Now it's Keir Starmer's (pictured, with candidate Kim Leadbeater) turn. After Boris's shock defeat in Chesham and Amersham, Labour is on course for another Red Wall by-election disaster, this time in Batley and Spen
Before I spoke to him, I was forwarded a message circulating on WhatsApp groups within the Muslim community. Listing '5 reasons why every citizen should NOT vote for Kim Leadbeater, the Labour candidate' it says, '1) She is a lesbian and will push the LGBTQ agenda in our town.' Galloway categorically denies involvement in those texts. 'That's completely untrue,' he claims, before pointing out that his most senior campaign worker is herself gay.
But someone is dripping poison into this campaign.
The same WhatsApp messages targeting Leadbeater also warn: 'Her party leader Keir Starmer is pro-Israel and pro-Zionist. He needs to get a clear message in Batley and Spen.'
Galloway campaign staffers also claim members of the Muslim community have been expressing concern to them over the fact Starmer's wife is Jewish, and that their children are being raised in the Jewish faith. Though again, they are unable to say who is circulating this information.
To Starmer's numerous critics on the Left, it doesn't really matter. Ever since the by-election was called, a cavalcade of Corbynite commentators and activists have journeyed from North London to the North of England. And they have all been pumping out the same message. Labour was wrong to turn its back on Jeremy Corbyn. Labour was wrong to dial down its campaigning on behalf of the Palestinians.
And these dual betrayals are about to cost them dear.
Which is half-right. Starmer is indeed on course for another crushing defeat, but not for the reasons the Corbynites claim. Starmer's change of stance on Palestine hasn't cost him votes in Batley and Spen, because he hasn't changed Labour's stance at all. 'There has been no significant policy shift on Palestine and Israel since the Election,' a spokesman for Shadow Foreign Secretary Lisa Nandy told me.
'We haven't changed anything,' a Starmer spokesman confirmed.
What he has done is suspend Jeremy Corbyn for his refusal to fully accept the findings of the EHRC report into Labour antisemitism, and finally spoken out against the racism blighting his party.
In turn, this has been weaponised by his hard-Left enemies. Their claim he has 'turned his back on the Palestinians' is really just a dog-whistle to the racists who flourished under Corbynism and are finally feeling the heat.
There are actually two reasons why Labour is set to lose. One – as Galloway identified – is the erosion of Labour's white working-class base. This is the reason for the pivot in his campaign strategy. When he filed his nomination papers, his ambition was to siphon off sufficient Muslim support, deliver the seat to the Conservatives, and end Starmer's leadership. But he now believes he can attract enough white working-class votes to snatch the seat.
The other is the totally bankrupt strategy Labour has pursued for a decade or more.
As Labour's grip on its traditional base weakened, it came to cling more and more desperately to those parts of its constituency that were sticking with the party. In particular, its Muslim supporters.
That's partly how Corbyn came to be elected Labour leader in the first place. It's how he was able to continue to brush the infestation of antisemitism within his party under the carpet. And it's why that party proudly waved the Palestinian flag at its annual conference while simultaneously branding as racist anyone who waved the Union flag.
That's the real reason Labour is heading for defeat in Batley and Spen. It's just the latest twist in its political death spiral.
Support among its traditional base continues to collapse. Labour tries to arrest its decline by frantically grasping for the Muslim vote. This further alienates its white working-class vote. And the plummet toward oblivion accelerates.
There is no one in politics more skilled at exploiting this reality than George Galloway. 'I'm going to win,' he told me. He may well be right. And if he does, Labour has no one to blame but itself.
How is it they have placed themselves at the mercy of this carpetbagger? How have Her Majesty's Official Opposition arrived in a position where their fortunes in a West Yorkshire by-election are inextricably linked to what is happening on the Gaza Strip?
I wrote a few weeks ago that if Starmer wants to begin to win back the Red Wall, he has to shut up about the Palestinians. But he can't. His party can't. They're too scared. Of George Galloway. Of the Corbynites. Of whoever is currently knocking on the doors of Batley and Spen and quietly whispering: 'By the way, you know that Keir Starmer? His wife is Jewish. And their kids are Jewish too.'
If Labour loses in Batley and Spen it won't necessarily mark the end of Keir Starmer's leadership. But looking at the poison seeping out of that by-election, maybe it would be better for him if it did.