Kerry insisted that Trump’s assertion that he “never walked away from the table” during the 2015 negotiations was false, saying, “I did walk away” during the talks.
“Unfortunately, and I say this sadly, more often than not, he really just doesn’t know what he’s talking about,” Kerry told CBS’s “Face the Nation.” “He makes things up. And he’s making that up as he has other things.”
Kerry drew Trump's ire in May after it was reported he had quietly been meeting with world leaders as an attempt to save the Iran nuclear deal ahead of its renewal deadline. Trump railed against Kerry on Twitter, saying the former State Department head "had his chance and blew it", accusing him of "hurting" the US.
Kerry said Trump's claim that the Iran deal is weak and harmful to the US is false and disruptive to the possibilities of international nuclear policy.
Kerry pointed to the fact that China, France, Germany and Britain have all tried to keep the deal in place.
"Only the United States walked away. Only Donald Trump," Kerry said. "His defense secretary thought he should keep it, his intelligence people thought he should keep it. The fact is this agreement is working."
He added that his defense of the policy wasn't a hit at Trump, but was in the best interest of US involvement in a positive policy.
"I was trying to have the policy of the United States of America, which is part of the agreement, to continue, and common sense to continue," he said.
Trump announced the US withdrawal on May 8, pledging to reinstate the sanctions on Iran and impose "the highest level" of economic bans on the country, jeopardizing the survival of the landmark accord.
Washington reinstated a series of unilateral sanctions against Iran in early August and would reimpose a second batch in November, primarily aimed at undermining Tehran’s oil exports.