American presidents have greater leeway on foreign policy than on domestic issues. Just see how President Obama is forging ahead to an agreement with Iran opposed by large majorities in Congress and among voters.

A president’s personal predilections and core assumptions can have much more of an effect on his foreign policy than on domestic issues. You can draw a straight line from Obama’s 2008 judgment that Iraq was a “stupid” war to the decisions that have led to the mess we see there today.