The answer is, with some difficulty.
Reports suggest there are two key themes to Boris Johnson's defence: first based around the complexity of Downing Street as both an office and a home; the second around the idea that work meetings often took place in the garden and stretched long into the evening.
The latter was the point put forward by former chief strategist, Dominic Cummings, in his recent blog. He argued that it was sensible to hold meetings outdoors and said at times these stretched into the evening and drinks would be brought out.
I think people will still find that hard to stomach when it comes to the picture of him and others - including the prime minister- sitting at a table devoid of notebooks or laptops, and with cheese and wine.
But it doesn't come close to the Reynolds' email - which is explicit that this is a social event - at the very time that people were unable to hold the hands of their dying loved ones (not to mention the cancelled weddings/parties/social events up and down the country).
There is no way to justify that as a work meeting, and nor is there anyway for Johnson to argue he just happened to be in his garden with his wife, to try to separate himself from the event.
Did Downing Street just think that because it was running the country, it was in a bubble where the rules didn't and couldn't apply?
Given that two days later the story of Cummings' story of his Durham trip broke- some are now asking if the May 20 party is the reason the PM defended his chief aide so fully at the time. Especially if - as he has suggested - Cummings told Reynolds the drinks were a bad idea.
For Labour, which now has an Urgent Question put to the PM, one issue is Sue Gray's inquiry for which no terms of reference have been published.
Pressure is intensifying on the prime minister and he won't be able to keep a low profile for much longer, reports ITV News Political Correspondent Romilly Weeks
The party wants a guarantee that this will all be looked at - and also that the buck won't stop with officials. "The culture starts with the PM," said one source.
Another question surrounds the Metropolitan Police - and its role - not least given how many people have faced charges for breaking lockdown rules.
And there is little question that rules were broken. As one person working in Number 10 during the same said to me, "I'm so angry- it's blatantly obvious it breaks the rules".
If the police get involved, does that put a break on Gray's internal inquiry, and then what?
One major issue (and in fact the thing that allowed this to get so bad in the first place) is the way that No 10 has handled allegations.
I've personally twice asked Prime Minister Johnson - in pool interviews on behalf of broadcasters - about parties.
The first time - on the alleged December 18 party - I asked why he didn't make the story go away by explaining how guidelines were followed - and he just repeated again - that he'd been assured guidelines were followed.
Later, when I asked about the picture of cheese and wine in the Guardian - he said it was people at work, discussing work.
And he repeatedly denied that there had ever been social events in Downing Street that he knew of, despite, it seems, having been at one.
For all that, the general feeling is that Reynolds and perhaps others will have to go, while the PM will survive, as he always does.
But it's hard to see how Gray could come to a conclusion that doesn't point the finger at Johnson himself. And that must then have some consequence.