Saudi Arabia has so far shunned direct participation in Donald Trump's war, keeping previous strikes on Iranian targets secret. But on Tuesday night, the kingdom joined US forces in carrying out a series of air strikes on Iranian proxy-groups in Iraq. On Tuesday, the Houthis fired ballistic missiles at a Saudi oil tanker attempting to cross the 14-mile chokepoint off Yemen's southwestern tip, in one of several recent attacks. They "acted very professionally and smart", Mr Trump said, in choosing to remain on the sidelines for the first five months of the war. Now, thanks to Mr Trump's war, Saudi Arabia faces the same conundrum in another critical waterway a few hundred miles to the west.