The Iran deal has never been the law of the land because it was never ratified as a treaty by the Senate (or enacted as statutory law by Congress). President Trump had every right to withdraw the U.S. from what was effectively an Obama executive agreement.
The damage done by the Iran deal has been significant, mostly due to the massive cash infusion the deal gave to the Khamenei regime and particularly to the IRGC. Imposing sanctions can reduce the flow of money to the regime.
The only way to deal with a maniacal regime like Iran is from a position of strength. Giving unilateral concessions in the hope of engineering better behavior will not work when a regime is dedicated to a totalitarian and suicidal ideology.
