Weapons proliferation

Democratic presidential candidate former Vice President Joe Biden speaks about foreign policy at The Graduate Center at CUNY, Thursday July 11, 2019, in New York. (AP Photo/Bebeto Matthews)

From left to right, spokesman for Iran's atomic agency Behrouz Kamalvandi, Iran's government spokesman Ali Rabiei and Iranian Deputy Foreign Minister Abbas Araghchi, attend a meeting in Tehran, Iran, Sunday, July 7, 2019. The deputy foreign minister says that his nation considers the 2015 nuclear deal with world powers to be a "valid document" and seeks its continuation. (AP Photo/Ebrahim Noroozi)

In this photo released by the office of the Iranian Presidency, President Hassan Rouhani speaks in a cabinet meeting in Tehran, Iran, Wednesday, July 3, 2019. Rouhani warned European partners in its faltering nuclear deal on Wednesday that Tehran will increase its enrichment of uranium to "any amount that we want" beginning on Sunday, putting pressure on them to offer a way around intense U.S. sanctions targeting the country. (Iranian Presidency Office via AP)

President Donald Trump talks during a signing ceremony in the Oval Office of the White House in Washington, Monday, July 1, 2019, with Vice President Mike Pence, left, and Secretary of Health and Human Services Alex Azar. The president signed a $4.6 billion aid package to help the federal government cope with the surge of Central American immigrants at the U.S.-Mexico border. (AP Photo/Carolyn Kaster)

President Donald Trump walks to the North Korean side of the border with North Korean leader Kim Jong Un at the border village of Panmunjom in the Demilitarized Zone, Sunday, June 30, 2019, in North Korea. (AP Photo/Susan Walsh)

President Donald Trump and North Korean leader Kim Jong Un walk together at the border village of Panmunjom in the Demilitarized Zone, in North Korea, Sunday, June 30, 2019. (AP Photo/Susan Walsh)

U.S. President Donald Trump, left, and South Korean President Moon Jae-in, right, pose for a photo during a visit to the tea house on the grounds of the Blue House in Seoul, South Korea, Saturday, June 29, 2019. Trump is making a quick trip to Seoul after attending the G-20 summit in Osaka, Japan. (AP Photo/Susan Walsh)

South Korean President Moon Jae-in, right, and U.S. President Donald Trump arrive for an expanded meeting at the presidential Blue House in Seoul, Sunday, June 30, 2019. (Kim Hong-Ji/Pool Photo via AP)

FILE - In this April 27, 2018, file photo, North Korean leader Kim Jong Un, left, prepares to shake hands with South Korean President Moon Jae-in over the military demarcation line at the border village of Panmunjom in Demilitarized Zone. U.S. President Donald Trump is inviting North Korea's Kim Jong Un to shake hands during a visit to the demilitarized zone with South Korea. Trump is scheduled to visit South Korea later Saturday after meetings at the Group of 20 summit in Osaka, Japan. (Korea Summit Press Pool via AP, File)