[Tomte]

Does the president need approval by Congress for lifting the sanctions? I don't know the answer, but I suppose that might be an issue.

[epc]

Congress must pass a bill to revoke the US sanctions, which is a separate act of legislation from assenting to this deal. There are several Executive Orders which Obama can revoke but the embargo proper is embedded in US legislation.

https://en.wikipedia.org/wiki/U.S._sanctions_against_Iran