Sanctions are one of the most powerful tools in the US toolbox short of war. In fact it's more important than war when dealing with Great Power adversaries because they have nukes. The US should aggressively block any attempt to get around it. Trump shouldn't have pulled out of the Iran deal, but preserving that power for the future is more important. Here's a good article about OFAC, the Treasury Department group th…
The ubiquity of US dollars in international trade allows US to torpedo the economy of any country it so desires. It is like the US has a kill switch to shut down any economy it wishes to. But the only reason the rest of the world plays along and allows the kill switch to exist is that they trust the US to use it responsibly and only in extreme circumstances. Now with the erosion of that trust, it is to be expected for the world to move towards eliminating that threat.