The sanctions name 700 Iranian individuals, companies and organisations, including oil producers, banks and shipping companies though not all of them. Some prominent banks and companies are not on the list.
He has also exempted some big oil customers, China, India and Turkey so as not to send world oil prices even higher. The exemptions mean Trump has additional weapons in reserve if he needs them. That has been his modus operandi with tariffs against China.
Trump believes that if he applies enough pressure Iran will negotiate a new nuclear deal with him, this time agreeing to cease supporting Shia militant forces such as Hezbollah in Syria and Houthi in Yemen.
Hezbollah, based in Lebanon, has been a menace to Israel but hardly represents a greater threat to that country than a nuclear armed Iran. The Houthi insurgency in Yemen is mainly of concern to Saudi Arabia, which ought to be no friend of a US President after its murder of journalist Jamal Khashoggi last month.
Quite why Trump has sabotaged a multi-national nuclear containment treaty with Iran for these purposes is not apparent. Many suspect he has done it for no better reason than the deal was done by President Obama and Trump had opposed it, as did Republicans in Congress.
The US House of Representatives has little say in foreign policy but if its voters yesterday can put a check on this President's power, many outside America will be relieved.