Paul R. Pillar
In Iraq, as in Syria, the imminent extinguishing of the mini-state of the so-called Islamic State (IS) is raising the question of whether U.S. objectives in Iraq really are focused on countering IS or will balloon into some other reason to keep American forces there indefinitely. The most common rationale voiced by those arguing for an indefinite stay is to counter Iranian influence. The rationale echoes larger alarms, being sounded by the Trump administration as well as others, about an Iran that supposedly is on the march and threatening to bring most of the Middle East under its sway. The alarms are filled with unsupported zero-sum assumptions about what any Iranian action or influence means for U.S. interests.
http://nationalinterest.org/blog/paul-pillar/iraq-iran-sharing-neighborhood-22937
