AURORA, Colo. — Independent presidential candidate Robert F. Kennedy Jr. said in a speech Sunday that the U.S. president should be sitting down with foreign adversaries for negotiations, name-checking Russia’s Vladimir Putin, China’s Xi Jinping and former Iranian President Mahmoud Ahmadinejad, who hasn’t been in office for over a decade.

The comment came on a day when the Iranian president since 2021, Ebrahim Raisi, dominated global headlines following his death in a helicopter crash…