An important detail in this long read from Al Monitor, which asked 2020 candidates about rejoining the Iran deal:

Longshot candidates Wayne Messam, a mayor from Florida, and spiritual leader Marianne Williamson also said they would return to the deal, with Messam vowing to make it a priority. Other Democratic candidates have been more evasive.

“My concern right now, my focus, is the denuclearization of Iran,” said New Jersey Sen. Cory Booker. “We need to be focused on best strategies to get us there. 2021 is a long time from now, and I’m focused on the steps we have to do right now.” The senator is a close ally of the pro-Israel lobby whose vote for the nuclear deal was long in doubt before he cast a decisive ‘yes’ vote for President Barack Obama’s signature foreign policy effort.

Diplomacy with Iran should be a top priority for the next president. Booker’s refusal here may be tied to his long-time close relationship with pro-Israel activists.