On the plausible assumption that the National Security Council decides on Wednesday that the poisoning of Sergei Skripal and his daughter constitutes an unlawful use of force by the Russian state on British soil, what response can and should the government make?
Talking to those involved in the decision, they say they face a tricky balance between taking action that Putin will notice versus leaving enough in reserve should Russia retaliate in some way.
So I am being guided that a number but not all Russian government staff based at its embassy in London will be expelled; and the ambassador will not probably be among those ordered to leave.
Some other Russian individuals close to Putin will be declared "non grata" and banned from entering the country. And they are likely to be deprived of access to any assets they hold here.
Being contemplated too is stripping Russia Today of its licence to broadcast here.
Also, we may deploy more troops and military hardware to territory close to the Russian border.
All of which may irk Putin to an extent, but he won’t lose sleep over them (if we launch a cyber attack against Putin, which is being mooted, that would certainly aggravate him, and would lead to retaliation - so it seems unlikely the UK would move there in the first instance).
So there is a recognition in government that if we could only secure the support of the rest of the EU and America, we could embarrass Russia with broader, more aggressive sanctions that might have an economic effect, on top of any embarrassment impact of punitive action by the UK alone.
That is easier said than done, however. Because as the prime minister is discovering as she embarks on a campaign of international diplomacy to secure overseas solidarity in any campaign we launch against Putin, the view of what happened overseas is not quite the same as the view from here.
In the UK, Theresa May and the government have highlighted the risk to many ordinary British people from the use of the nerve agent by whoever wanted to kill the Skripals: a policeman who came into contact with the weapon’s grade toxin was seriously injured; and hundreds of citizens in Salisbury, where the attack took place, have been told to wash their clothes and personal effects, just in case they’ve been contaminated by the nerve agent.
The view from Britain therefore is that this was an act of terrorism where the collateral harm to UK people could have been significant.
Outside the UK however the prism is slightly different; the atrocity is seen through the prism of a le Carré novel.
In other words it’s seen not as an act of aggression against the British people but the attempted bumping-off of a spy by another spy, or a tit-for-tat in the murky world of espionage.
So although Theresa May will try to get EU backing for broader sanctions, and although her colleagues think she will probably succeed, the UK may yet face Russia alone.