BRUSSELS—Mike Pompeo began his first overseas trip as secretary of state with the fate of the Iran nuclear agreement hanging in the balance, while tensions with Moscow have raised questions from the U.S.’s allies about Russian relations.
For the next two weeks, the fate of the Iran deal is set to be the largest issue looming over trans-Atlantic relations. European officials are fighting to preserve the agreement in talks with a new U.S. foreign policy team that shares President Donald Trump’s deep skepticism toward the 2015...