Only the naive would have been overly surprised at last week's decision by the Saudi-led Opec Plus, which includes Russia, to cut oil production at a time when the United States was expressly pressing for the opposite.

Predictably, the US has accused the Saudis of "siding with the Russians". There is talk that Washington may come down hard on Crown Prince Mohammed bin Salman, who recently took on the title of prime minister, with retaliatory measures and a "re-evaluation" of the US-Saudi relationship.