Sky News’ Lewis Goodall says the numbers are tight for Jeremy Corbyn to take over as a caretaker prime minister.
At the start of the year, the Lib Dem bird could barely flap its wings. It seemed on its way to meet its maker.
Yet with the sort of extraordinary alchemy that makes politics so beguiling, it took flight again.
They’ve had a stellar run – a great local election performance, equally good European elections and a crucial victory in the Brecon and Radnorshire by-election.
And political pressure accrues as the party’s importance grows.
Jeremy Corbyn’s intervention, in the form of a letter humbly asking his fellow opposition leaders to support him in a confidence vote, was the most astute bit of politics he’s executed for some time.
It successful transferred the Remainer burden of proof from him to the Liberal Democrats and other opposition parties.
Ms Swinson botched it.
She is right to be wary of appearing to embrace Jeremy Corbyn too firmly.
She does not want to transfer even a slither of Remainer credo to her rival.
She also has scores of Conservative seats in her sights, many of which might not take kindly to her installing Mr Corbyn into Number 10.
But if she was wise not to hug him too close, she was unwise to keep him at such a distance.
Ultimately, the Lib Dems can count their unexpected revivification from the coalescence of Remainers behind their banner.
Even in Tory seats, their only hope is to bring most or all of the Remainer vote in those seats behind them.
If they are seen, in any way, not to have explored every avenue for preventing no deal – including a Corbyn government – then they will pay a price.
Not least because, in the not-so-distant past, they spent five years arguing that they had to support a party and prime minister they did not much like in “the national interest”.
It would seem incredible to argue they couldn’t do the same again, for an emergency government, for little more than five weeks.
The problem for the anti-no dealers is that both Mr Corbyn and Ms Swinson are right.
Mr Corbyn is correct that, as leader of the opposition, he has the most legitimacy and credibility to try and form a new administration should Boris Johnson’s fall.
Ms Swinson is right that the numbers are probably not there – even with Lib Dem support – to allow him to do so.
Ironically, that is not so much as a result of SNP, or Lib Dems or Plaid Cymru or the rest, but instead MPs, who until relatively recently, Mr Corbyn would have counted as his parliamentary colleagues.
There are around a dozen former Labour MPs who, for one reason or another, have been expelled or left the party in protest at his leadership.
Some have told me that they will vote against the government in a no-confidence motion but will not subsequently vote for Mr Corbyn.
Others, however, might not even go that far.
Chris Leslie, one of the Change UK MPs, told me on Thursday that his group of five might not even vote against the government in a confidence motion and instead focus on ways to compel it through law to abandon no deal.
If they hold true to their word it will be almost impossible to bring the government down, not least because it will be even harder to convince wavering Tory MPs to destroy their careers by taking the nuclear option of defeating their own government if they don’t think it has any chance of succeeding.
As I have written before, the reason the no dealers are dominating the political landscape is because they have unity of purpose.
They have one goal – to take Britain out of the EU on 31 October, deal or not.
That imperative sublimates all else and means they will countenance anything to achieve it.
The opposition, although nominally united against no deal, seems unwilling to relegate their other imperatives.
The easiest lever to pull would be to unite behind Mr Corbyn as caretaker but for myriad reasons they are reluctant are unwilling to do so.
Mr Corbyn, understandably, is equally reluctant to step aside as next in line for the premiership, even a caretaker one.
Wherever the blame for that lies, if no one budges, only half of a house divided, then they will all lose.