Trump announced Tuesday that he is walking away from the deal, which curbed Tehran's nuclear program in exchange for sanctions relief
. The decision, which Carter also referred to as "ill-advised," pits Trump against US allies, and leaves the future of the agreement under a cloud of uncertainty.
In announcing his decision, Trump said he would initiate new sanctions on the regime
, crippling the agreement negotiated by his predecessor, and he said any country that helps Iran obtain nuclear weapons would also be "strongly sanctioned."
This "may be the worst mistake Trump has made so far," Carter said.
"When a president signs an agreement, it should be binding on all his successors, unless the situation changes dramatically and it hasn't changed," he said. "Unfortunately, I think it signals a message to North Korea that if the United States signs an agreement, it may or may not be honored."
Carter, who has previously negotiated with the North Korean leadership
, spoke to Gupta before being honored at the Bill Foege Global Health Awards
. Carter and First Lady Rosalynn Carter were being recognized for their contributions in combating the spread of neglected infectious diseases on a global scale.
The awards are presented annually to recognize people and organizations who contribute to the progress of global health. Foege, the awards' namesake and a former director of the US Centers for Disease Control and Prevention
, worked on the successful campaign to eradicate smallpox
in the 1970s.
Carter's work in foreign affairs didn't end after his presidency.
For decades, the Carter Center has worked with ministries of health in nations worldwide to track tropical disease cases and to help stop the spread of those diseases by providing health education and programs.
In March, the Carter Center and MAP International worked with the Liberian Ministry of Health to form a new partnership to combat a growing mental health crisis in Liberia
. Their efforts included providing neuropsychiatric medications and supplies to the country, where decades of civil war and the outbreak of Ebola have left behind psychological scars.
Carter gave credit to his wife for the advances made in Liberia.
"There's no doubt that the Liberians have responded well. We now have trained about 250 or more mental health technicians, and we have them scattered all over Liberia," he said.
The Carter Center also has made progress in efforts to eradicate Guinea worm disease infections.
So far this year, only one country, Chad, has confirmed human cases of Guinea worm disease in three people
. For all of last year, there were 30 Guinea worm cases
, evenly split between Chad and Ethiopia.
Guinea worm disease is a parasitic infection
spread through drinking water from ponds or other stagnant water containing Guinea worm larvae. In 1986, Guinea worm disease afflicted an estimated 3.5 million people a year
in 21 countries across Africa and Asia.
Carter often has said that his goal is to outlive Guinea worm.
In the summer of 2015, Carter announced that he had been diagnosed with a deadly form of skin cancer called melanoma
, which spread to his brain. He was treated with a combination of surgery, radiation, and immunotherapy
-- and now he says he is doing well
. He said his doctors have not used the word cure but say he is still in remission.
"I still get a check-up every three months or so, brain scans and things like that, but so far the results have been good," Carter said.
"I still hope to outlive the last Guinea worm," he said.
CNN's Nicole Gaouette and Kevin Liptak contributed to this report.