It has been the proverbial tit-for-tat measure in diplomacy. The thaw in the Cold War frost, markedly in evidence ahead of Donald Trump’s election and thereafter, has been reversed with Sunday’s imprimatur from the Kremlin to the White House.

In an aggressive response to the latest cache of US sanctions against Russia, Iran, and North Korea, Vladimir Putin has ordered that the American diplomatic mission in Moscow must truncate its staff by 755 employees and no less. So drastic a diplomatic reprisal ~ after having batted for Trump in the elections ~ was almost inconceivable.

Which is why it is said to be reminiscent of the “Cold War playbook”. While a parting of the ways is improbable in contemporary international relations, the twin developments are bound to ratchet up ternsions between Moscow and Washington, and a mending of fences is unlikely anytime soon. Putin has couched his action with the blunt remark that “Russia had run out of patience waiting for relations with the United States to improve”.

Now that his meddling in the US elections has been fairly established and Trump has his back to the wall, neither the Republicans nor the Democrats will want ties to improve.

The US President has lost the political battle at home; the trans-Atlantic wound shall fester for a long while yet. “Over 1,000 employees, diplomats and technical workers are stationed in Russia; 755 will have to stop this activity,” is the text of Mr Putin’s order.

“That is biting.” The efficacy of sanctions as a method of reprisal is open to question yet again. Far from playing on the backfoot, these curbs have strengthened the Kremlin’s resolve to hit back.

The souring of relations has happened in the aftermath of the G-20 summit in Hamburg. Mr. Trump had talked during his campaign of improving ties with Russia, praising Mr. Putin. The Kremlin had anticipated that the face-to-face meeting of the two Presidents would be the start of a new era.

The immediate assessment in Moscow was that the two leaders had set the stage for better relations. Far from it, as the weekend’s developments testify. First came the sanctions passed by Congress, followed by President Trump’s indication that he would sign them into law, and now Moscow’s robust retaliation.

The measures, both the sweeping sanctions and the order to reduce diplomatic staff at another remove, add up as the harshest moves since a similar rupture occurred in 1986 in the twilight phase of the Soviet Union, which disintegrated in August 1991. Twenty-six years later, the shadow-boxing is a faint echo of the Cold War.

And the chief cause for surprise must be that the rupture has occurred after a bout of almost simulated flirtation. In a remarkable sense of timing, Russia has struck back after Congress voted the sanctions, but before Mr Trump signed them into law.