I have sat through many days of the Covid-19 Inquiry and listened to extraordinary, sometimes jaw-dropping detail about what went on in government during the pandemic.
A picture has been painted of a dysfunctional Number 10, slow and confused decision making, and a toxic culture spilling out in furious misogynistic WhatsApp messages.
All of which leaves the man in charge at the time, Boris Johnson, with a number of difficult challenges when he gives evidence this week.
Was he too slow to lockdown?
Perhaps the biggest question the former prime minister will have to address is whether he was too slow to act in imposing national lockdowns.
Not just the first one in March 2020, but the subsequent one in autumn and then January 2021.
The inquiry has heard allegations that the then PM simply didn't take Covid seriously enough as it spread across the world. He didn’t attend the first five emergency meetings - also known as COBR meetings - and supposedly took a 10-day half term holiday in February 2020.
During that time Italy imposed its first local lockdowns. It wasn't until March 2 that Mr Johnson chaired COBR. By that time, the UK had already recorded its first Covid-19 death.
That same day, Mr Johnson's then chief adviser Dominic Cummings said in a WhatsApp message: "The PM doesn’t think it’s a big deal. He doesn’t think anything can be done and his focus is elsewhere. He thinks it will be like swine flu."
It wasn't until March 23 that the PM finally implemented a full lockdown.
The former health secretary, Matt Hancock, testified that the delay, in his view, cost tens of thousands of lives.
Covid Inquiry: 'Many lives' could have been saved by earlier lockdown
In his defence, Mr Johnson is likely to argue that behavioural scientists were suggesting there was a danger the public would tire of heavy restrictions.
But the rationale for delaying the second lockdown might be harder to explain away. Sir Patrick Vallance and Sir Chris Whitty, both chief advisers to the government during Covid, have made it clear they were arguing for a circuit breaker lockdown from September 2020.
There has been plenty of evidence to suggest Mr Johnson oscillated between different views and at times showed a disregard for the death toll amongst the elderly.
An extract from Sir Patrick's diary in October 2020 read: "PM Meeting - [he] beings to argue for letting it all rip... they have had a good innings."
Even more damagingly, the inquiry has also heard confirmation from his aide at the time, Lord Edward Lister, that Mr Johnson did say the long reported, often denied phrase, "that he would rather let the bodies pile high than impose another lockdown".
Did he understand the science?
Part of the problem, some witnesses allege, is that Boris Johnson simply didn't understand enough about the science to take effective decisions.
Sir Patrick's diaries have provided a valuable insight here. On May 4, 2020, he said the "PM is clearly bamboozled", while the next month that "watching the PM get his head around stats is awful".
A toxic culture in Downing Street?
The former prime minister will also face scrutiny over accusations of a toxic culture in his Downing Street operation.
Dominic Cummings in particular seems to have been given free rein. WhatsApp messages seen by the inquiry reveal him calling ministers "morons" and "useless ****pigs".
The former chancellor Sajid Javid has been among those claiming the former chief adviser sought to act as prime minister in all but name, telling the Inquiry: "Many times I felt that the key decisions were being made by Mr Cummings and not the PM, in a way I hadn't seen with any other PM."
'The extent of dysfunctionality was something I had not experienced before in any government', Sajid Javid tells the Covid-19 Inquiry
Will he apologise for Downing Street parties?
And then, of course, there is Partygate.
So far, Mr Johnson has only apologised for not realising his actions would constitute a breach of the rules, not for actually attending one of the events, or for the culture that allowed them to happen.
The lead counsel to the inquiry, Hugo Keith KC, is unlikely to miss an opportunity to ask the former prime minster to explain his actions.
But he has been preparing hard for his appearance.
I’m told he's been working with his lawyers intensively over the past few weeks, going through a huge amount of paperwork. His central argument will be that his government got the big calls right given the information they had available to them at the time.
On the timing of the first lockdown, for example, he is likely to point to advice he was receiving in March that there could be lockdown fatigue if the government moved too early.
Mr Johnson’s view is that as prime minister he had to arbitrate between competing priorities.
On the occasions when it appeared that decisions were changing, he will argue, that was often because the underlying scientific advice had shifted.
I also understand there might not be as much mud-slinging as we have had from some witnesses. He is said to barely mention either Dominic Cummings or even Rishi Sunak in his witness statement.
As for his view of the parties in Number 10 - his position has not changed.
He will apologise for areas where the government fell short.
There will be many people hoping for some sort of catharsis tomorrow - but they might not get it.
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