For months Vladimir Putin has been in a truculent mood. Ever since he attacked the US and Nato at the Munich security conference in February for trampling on his national interests, he has been spoiling for a fight. Although he is not allowed to stand for re-election next year, he knows the nationalist card plays well with Russian voters. His allies in the state duma will benefit. So will his protégé for the presidency, whoever that may be. But the rest of the world should be careful not to overreact.

On Saturday Mr Putin signed a decree suspending Russia's role in the Conventional Forces in Europe treaty, which limits the number of tanks, artillery and combat aircraft that can be based between the Atlantic and the Urals. He had already threatened to do so in retaliation for US plans to site missile defence installations in Poland and the Czech Republic. It is a negative gesture, although it may make little difference in the real world. Nobody wants to restart an arms race, not even Mr Putin. But abrogating the treaty will stop arms inspections and undermine confidence. Nato should regret the gesture, but not seek to retaliate. That would be playing Mr Putin's game.