Iran has long asserted that it can shut down the Strait of Hormuz. While the strait can't be "closed" in the traditional sense - like shutting a road - Iran could attempt to make the waterway too dangerous for commercial passage, effectively disrupting global shipping.

Pentagon officials are trying to prepare for all of the ways Iran could retaliate, as President Trump hints at what he might do.

Iran could shut the Strait of Hormuz as a way of hitting back against its enemies, a senior lawmaker said on Thursday, though a second member of parliament said this would only happen if Tehran's vital interests were endangered.