Nikki Haley said the US was not saying that Iran was in breach of the agreement, but she raised concerns about its activities that are not covered by the pact.
Richard Cowan and David Morgan
The plan would lower corporate and small-business income tax rates, reduce the top income tax rate for high-earning American individuals and scrap some popular tax breaks.
As Republican moderates hold out for fear of receiving backlash from voters, this puts Trump in danger of his second major legislative setback.
Trump’s criticism of Khizr Khan and Ghazala Khan, who took the stage at last week’s Democratic convention, sparked growing concern and dismay from Republican lawmakers responding to the latest Trump outburst to blindside his party colleagues.