Under U.S. law, Trump must decide by Oct. 15 whether to recertify Iran's compliance with the agreement. The International Atomic Energy Agency, which has inspectors in Iran to monitor its nuclear facilities, has said eight times that it is complying. If Trump does not recertify it, as he has repeatedly suggested he will not, Congress will have 60 days to decide whether to reimpose U.S. sanctions that were lifted when the deal took effect. That would in effect be a withdrawal.