New Delhi, April 15 -- The black market for Iranian oil wouldn't exist without China. Before the Iran war began, Beijing bought 95% of all the crude Tehran shipped via a network of sanctioned tankers and shadowy financial links. Hence, US President Donald Trump isn't just targeting Tehran with his blockade of the Strait of Hormuz-he's aiming at Beijing too.

On Monday, the US said vessels in Iranian waters would be subject to "interception, diversion and capture." If its navy enforces a blockade on ships entering and departing Iranian ports and coastal areas east of the Strait of Hormuz in the Gulf of Oman and Arabian Sea, Tehran won't be able to export a single barrel of oil.

America's calculus appears twofold: first, impose an intolera...