Retaliate how, exactly, and what will be the threshold of proof? UK foreign minister Boris Johnson told Parliament today that the verrrrrry suspicious sudden and simultaneous illnesses of Sergei Skripal and his daughter Yulia were, um, verrrrrry suspicious. Johnson brought up the obvious parallels to the slow 2006 assassination of former Russian spy and Putin critic Alexander Litvinenko and warned Russia that the UK would respond “robustly” if they are responsible for the attack yesterday.

But what would that retaliation be? It might involve some ball-kicking, but not in the sense one would expect:

The UK will “respond appropriately and robustly” if if the Russian state is found to have been involved in and in Salisbury on Sunday, Boris Johnson has said, including reconsidering its participation in the 2018 World Cup.

The foreign secretary said it was “very difficult to see how UK representation at that event [the World Cup] could go ahead in the normal way” if Russian state involvement was proved, though a Foreign Office source said that was not a reference to the England team’s participation. …

“It is too early to speculate as to the precise nature of the crime or attempted crime that has taken place in Salisbury,” he said. “But I know members will have their suspicions.

“If those suspicions prove to be well-founded then this government will take whatever measures we deem necessary to protect the lives of the people in this country, our values and our freedoms.”

Russia will host the World Cup in June of this year, which — like the Sochi Olympics in 2014 — will undoubtedly be used by Vladimir Putin for propaganda purposes. That will make it like every other World Cup and Olympics, of course, but any kind of tarnish on the event will not make Putin happy. Unless the UK organizes a large-scale boycott, though, the UK’s absence won’t make that much of an impact. Even a large-scale boycott won’t matter much, though, as the reflexive US and Soviet Olympic boycotts in 1980 and 1984 proved.

There are other options available, of course, but the UK won’t be looking for a literal eye for an eye. They can expel Russian diplomatic personnel and arrest other known intelligence operatives without diplomatic cover in order to get the message to Moscow. The US did the same thing at the end of 2017 in a rather impotent action, well after the Obama administration knew of their election meddling, but it still represents some kind of direct response to malicious activity.

Johnson told Parliament that he had more options in mind for dealing with Russian cyberwarfare, which he says has reached the level of hostilities between the two nations:

Johnson said the UK government increasingly viewed Russian cyber-attacks as “acts of war” against Britain. “That means that we need to elaborate a new doctrine of response and a new doctrine of deterrence as well, and we certainly are. That is one of the conclusions that we took in the NSC [national security council] a few months ago,” he said.

Skripal and his daughter remain alive for the moment, in critical condition. Thus far the UK has not announced what the “unknown substance” was that nearly killed them, but they’re worried enough about it to send samples to a military lab and to keep one member of the first-responder team in the hospital under observation. Whatever it was, it had a dramatic impact on both victims:

Skripal is fortunate he didn’t choke to death on his own vomit, although that fortune would only count if he survives this attack. NBC spoke with a former MI6 agent who believes this has all the hallmarks of a Russian hit on a turncoat:

While there is no evidence of any Kremlin connection in Skripal’s case, intelligence analyst Glenmore Trenear-Harvey, who formerly worked for MI6, told NBC News he believes the case has the hallmarks of Putin’s involvement.

“For this to be in a shopping mall, for this to be in public, and for the fellow himself to be a former intelligence officer, immediately one looks to potential attackers, ultimately that would be as the result of President Putin authorizing it,” Trenear-Harvey said, adding that the incident could serve as a warning to any dissidents within Russian security forces that “it might take some time, but we will get you.”

Richard Walton, a former head of London’s Metropolitan Police’s counter-terrorism command, cautioned against jumping to conclusions but highlighted that relations between the U.K. and Russia were already near the “breaking point.”

“The investigation must take its course, but if this is state-sponsored terrorism and it looks entirely possible, then it will have grave consequences,” Walton said during an appearance at the Security and Counter Terrorism Expo in London.

Thus far, the UK has released no information about suspects. Surveillance footage of Skripal and his daughter has emerged, but it doesn’t show the attack or its aftermath. They may not have much unless one or both victims recover from the attack, but identifying the substance will go a long way to determining who backed the attack.

Update: I mixed up the order on the Olympic boycotts; it’s been fixed now, thanks to Steve Eggleston.