President Trump has not yet pulled America out of the 2015 Iran nuclear deal. But he just took a vital step toward doing so, in a landmark speech on Friday that in plain language dismantled the dangerous fictions on which the deal was built. Chief among these fictions is the notion that a nuclear program in the hands of Iran’s predatory, terror-sponsoring Islamist regime could ever be “ exclusively peaceful .” This was a phrase repeated endlessly by President Obama’s diplomatic team during the negotiating of the Iran nuclear deal, and it is enshrined in the final text, as if...