The Iran deal in particular was closely negotiated over the course of years. Iran gave up 90% of its nuclear enrichment program in return for an end to economic sanctions. While the other member states of the UN Security Council did lift UNSC sanctions, the Republican-controlled Congress not only did not lift unilateral US sanctions but actually slapped more on.
Or take Canada. As I wrote on Friday:
Trump also repeatedly insists that the US runs a large trade deficit with Canada, importing more goods from that country than it sells to its northern neighbor. Those in the US who make that argument are typically counting third party goods imported into the US through Canada, which Ottawa considers an unfair accounting. The fact is that the US-Canada trade is almost equal, and if you count both goods and services, it is the US that runs the surplus.