There is a hobby raising giant pumpkins. To grow to giant size, the vines must be large in diameter because the water flow through the vine is enormous while the pumpkin is growing.
Be placing a band around the vine, diametric growth is prevented. Water doesn’t flow, the pumpkin fruit withers.
Trump put a band in the form of sanctions on the Iranian vine. Iran is in fact withering on the vine
Iran is pretty much a one crop economy - oil/gas exports.
They manufacture little of what the consume, and have to import food. The economy is overwhelmingly controlled by the Revolutionary Guards Corps (Pasdaran) and large trusts (Bonyads), which were traditional islamic charitable foundations, now perverted into large holding companies for corrupt mullahs. It is a highly rigged, unproductive system.
The Government is overwhelmingly funded by oil revenues. The last round of sanctions, imposed in May, are designed to take their legal oil exports down to zero.
It is likely going to get a lot worse there, as reserves run out. No need to fight the regime, when it is already bleeding out.
Maduro in Venezuela too. Chinese communists heading that way too. North Korea is under hard sanctions too.
President Trump has just stopped pretending that those regimes are OK, or equally valid, or whatever other Leftist bull crap.
They are cut off, and going broke.