Unlike his predecessor, George W. Bush, who styled himself as “the Decider” and took pride in sticking with decisions come what might, Obama is emerging as a leader so committed to pragmatism that he will move to a new position with barely a shrug.

Whether it’s a long-standing campaign promise or a recent Oval Office decision, Obama has shown a willingness to reverse himself and even anger his most liberal supporters if he can advance a higher-priority goal or avoid what he sees as a distracting controversy.

“This is the story of an ambitious new administration running up against reality at home and abroad,” said William A. Galston, a senior fellow at the Brookings Institution and former advisor to President Clinton. “The realities on the defense and foreign policy fronts are both more intractable and quicker to show themselves for what they are.”