US President Barack Obama has secured enough support in the US Senate to ensure that the Iran nuclear deal will go into effect.
Democrat Barbara Mikulski of Maryland became the 34th senator to back the deal on Wednesday.
US Congress could still oppose the deal, but Mr Obama has now enough votes to override any resolution of disapproval.
He has said the deal cuts off "every pathway to a nuclear weapon" for Iran.
"No deal is perfect, especially one negotiated with the Iranian regime," sad Ms Mikulski in a statement. "I have concluded that this Joint Comprehensive Plan of Action is the best option available to block Iran from having a nuclear bomb."
Republicans have been unified in their opposition to the Iran accord, saying the deal would only "embolden" Iran.
Two Democratic senators - Chuck Schumer of New York and Robert Menendez of New Jersey -- are also opposed, as are a handful of Democrats in the House.
Congress is set to vote on the accord later this month, but the White House is hopeful it can secure seven additional votes to allow for a legislative move known as a filibuster.
A filibuster would prevent a final vote and Mr Obama would not need to use his veto power to keep the Iran deal on track.