Former White House officials who supported the killing of Soleimani this month viewed Mattis’s absence as one of the reasons the strike proceeded, surmising that Mattis either wouldn’t have supported such a strike or wouldn’t have presented the option to the president. Mattis declined to comment on the strike or advice he would have provided.

His caution was often backed up by the then-chairman of the Joint Chiefs of Staff, Gen. Joseph F. Dunford Jr., and then-White House chief of staff John F. Kelly, according to former administration officials. The trio for decades served together in the Marines and were focused on the possible ramifications of escalation in the Middle East…

The diminished threat posed by the Islamic State in Iraq and Syria has given Trump’s national security team license to shift its focus more toward Iran. Gen. Joseph L. Votel, who retired at Central Command, had been a chief architect of the Trump administration’s plan to destroy the Islamic State and a staunch advocate of keeping U.S. troops in northern Syria to support Kurdish forces and ensure the remnants of the Islamic State did not return.