JUSTIN WEBB: Jill Biden, the woman who holds the world's future in her hands this weekend

What is the mental state of Joe Biden this weekend? Not good, we can assume. For all the brave talk of carrying on, Thursday's calamitous presidential debate must cast a pall not only over the nation and the Democratic party, but also over the 81-year-old incumbent president himself.

Biden genuinely believes he is the only candidate who can beat Trump this year, even if half his party believe he is the only candidate who cannot. He believes that he has the mental capacity to carry on even if his body is slowing.

At a rally on Friday, he admitted that he is not the debater that he once was, but he is telling himself that does not matter.

He is telling himself he is still the great man he once was.

But all the places outside the White House that Joe Biden turns to for comfort and support are telling him the game is up.

American President Joe Biden pictured during the presidential debate on June 27

First Lady Jill Biden and American President Joe Biden pictured as they arrive to speak at a campaign event in North Carolina on June 28

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The news station MSNBC (the Left-wing equivalent of Fox) that he watches in the morning was positively funereal in the hours after the debate. The anchors looked as if they were announcing the end of the world. And then his beloved New York Times that he reads on an iPad every day. Every single opinion piece on Friday said the same.

These are his friends, in some cases actually pals of his, who have known him for decades. Pals such as the writer Thomas Friedman, who still sees the president one-to-one at the White House, whose article this weekend was titled 'Joe Biden Is a Good Man and a Good President. He Must Bow Out of the Race'.

Friedman suggests that the Biden family and political team should gather quickly and have what he called 'the hardest of conversations with the president, a conversation of love and clarity and resolve'.

Is his wife Jill ready for that conversation? There is no real doubt about the closeness of their bond. And her respect for his political life.

Joe Biden and First Lady Jill Biden pictured at a waffle house in Georgia after the presidential debate on June 28

This love and this care has been part of the Biden story. But there is a darker side that risks being accentuated now. A prominent conservative-leaning website ran an unflattering photo of the Bidens on Friday with the headline 'Cruel Jill Clings To Power'. A Republican congresswoman spelled it out: 'What Jill Biden and the Biden campaign did to Joe Biden – rolling him out on stage to engage in a battle of wits while unarmed – is elder abuse, plain and simple.'

These attacks can be managed when they come from opponents. But if the Democrats face losing the White House because their candidate will not agree to make way for a younger, more vigorous alternative, then the anger will surely start to come from Biden's own side. And it will be mighty anger. The Democrats believe that Trump is an existential threat to American democracy and must be stopped at all costs. The loss of the Biden family honour is a price they will gladly pay. These things Jill must weigh with her husband.

The Democrats believe that Trump is an existential threat to American democracy and must be stopped at all costs. The loss of the Biden family honour is a price they will gladly pay. These things Jill must weigh with her husband

My sense is that Jill, and Biden's younger sister Valerie, who has always run his campaigns, are going to be the only people who matter over the next few days. No one can shift Joe if Joe won't be shifted. Yes, Barack Obama and Bill Clinton could drop by. But it is highly unlikely they would speak publicly. Nor will any of his potential replacements want to break cover.

It REALLY does come down to Jill. The 73-year-old, who also teaches in community college, is said to enjoy the status that being First Lady brings, and will be naturally reluctant to relinquish it.

She has never held elected office but plenty of Democrats think she holds the future of the nation, and the world, in her hands this weekend. She has to decide. If she says go they will go. And she has very little time if the party is to recover and still beat Donald Trump.

Over to you, Jill.

Justin Webb presents the Americast podcast on BBC Sounds