Mattis's expression of support for the 2015 agreement curbing Iran's nuclear program was in sharp contrast with Trump's blunt assessment that the deal is an "embarrassment."
Asked during a Senate hearing whether he believed it was in the national interest, Mattis replied: "Yes, Senator, I do."
"If we can confirm that Iran is living by the agreement, if we can determine that this is in our best interest, then surely we should stay with it.