Pakistan, July 9 -- The ceasefire between the United States and Iran is under its severest strain yet. Speaking at a NATO summit in Ankara on Wednesday, President Donald Trump said the memorandum of understanding signed in mid-June was, as far as he was concerned, "over," though he left the door open for negotiators to continue talking. He also vowed to hit Iran hard after another flare-up around the Strait of Hormuz, the waterway that has again become the sharpest edge of this conflict.

The latest exchange has already gone beyond rhetoric. Three commercial vessels have been struck near Hormuz in recent days. The US has carried out strikes on Iranian targets, Tehran has retaliated against US-linked facilities in Bahrain and Kuwait, Washi...