WASHINGTON, Aug. 25 -- The instrument of American policy toward Iran this week is not a carrier group. It is a telephone. Scott Bessent told reporters on Monday that President Donald Trump is working through a list of foreign leaders, calling them individually with what the Treasury secretary described as specific requests to cease their interactions with the Iranian government.

The calls are the enforcement arm of something larger. Bessent used the same appearance to unveil what the Treasury has named Operation Economic Outcast, a campaign built almost entirely on secondary sanctions, meaning penalties aimed not at Iran but at everyone still doing business with it. He reached for a wartime comparison to describe it, calling the effort a...