NERVE gas on the streets of Salisbury is only the latest episode in an increasingly aggressive foreign policy by the Russians (News, 16 March). First, they seized Crimea and threatened Ukraine. Then, Moscow allegedly intervened in the United States’ elections, possibly tipping the vote towards Donald Trump. More recently, Washington has accused Russia of planning for attacks on the US’s critical infrastructure. Earlier this month, President Putin made a speech boasting of a new generation of “invincible” Russian nuclear weapons that could devastate the US, and showed a video animation of missiles raining down on the US by way of illustration. Then came Salisbury.

The Prime Minister was quite right to react robustly by expelling 23 Russian “diplomats”, even if it did invite an escalatory tit-for-tat response from Moscow, which also closed the British Council and the UK consulate in St Petersburg. We have not always been so forceful.

Last year, the news website BuzzFeed ran a big story reporting that the successors to the KGB might well have been responsible, in recent times, for the mysterious deaths of some 14 or 15 opponents of President Putin in the UK. The British police denied that they had prematurely closed investigations into the cases at the behest of the Government, whose realpolitik was untroubled by one group of Russian gangsters’ bumping off another group. It is certainly true that the assassination of the former KGB agent Alexander Litvinenko, in 2006, was met by a fairly feeble response from the British authorities.

So, what has changed? Perhaps it is that the reckless use of poison gas in a small British cathedral city threatens ordinary British people, too. Reports in the American press suggest that as many as 38 individuals in Salisbury have received some kind of treatment since the incident. Perhaps it was the brazen sarcastic insolence with which the Russians responded when it was revealed that the poison was of a kind produced in the Soviet bloc in the 1970s and ’80s.

But, after responding firmly, it seems important now to pause prudently. It is possible that all this muscle-flexing was a strategy by President Putin to ensure the landslide election victory that he secured on Sunday. Despite the stuffing of ballot boxes, and the banning of his main election rival, it seems clear that a majority of the Russian population support him. It is possible that, having got what he wanted, he will now ease off the strongman stunts. It was noticeable that, immediately after his re-election, he warned that cuts in Russia’s defence budget would come this year and next. His priority, he said, was to grow the economy.

International analysts are sceptical that President Putin can achieve that without strengthening the rule of law, and, in particular, competition law, which would hit his racketeering cronies particularly hard. Even so, it is worth waiting to see what transpires. Leaders with domestic problems often turn their attention to foreign-policy adventuring. If Mr Putin does that, it may well be that we will have to strengthen economic sanctions, or set up an alternative World Cup.

But, for now, a period of calm reflection would seem sensible.