In other words, his war has failed to achieve any meaningful objective so he is falling back to idle economic threats.
I'm sure China is now shaking in their boots since they are the biggest buyer of Iranian oil.
America has tried this with Cuba too (the 'Helms-Burton Act', I think), but they've only been successful in making it stick in very limited circumstances (mostly to companies who are technically foreign-owned but which primarily operate in the US).
Last time I checked, Russia, China and North Korea are doing business with Iran. Come on big guy, take these folks on. But then, this would probably cost Trump money and increase his personal risk. But the US lived there for decades.
U.S. President Donald Trump announced what he called the “most crushing economic operation ever taken” against Iran on Wednesday, threatening sanctions against any country that continues trade or financial dealings with Tehran as a nearly six-month-old war between the two countries remains deadlocked.