What the historians are suggesting, however, is that the modern president may simply not be able to exercise that same firm grasp — or at least not most of the time. With global interdependence comes a certain lack of control, a vulnerability to disparate influences beyond our territorial borders that are less obvious and less easily answered than the launch of a Soviet satellite. And those influences, perhaps, directly undermine our ideal of what a president should be.

We are susceptible to presidents who talk with the self-assuredness of a Western movie sheriff or who, like Mr. Obama, seem to project an aura of celebrity or historic greatness. But we are disappointed when they inevitably turn out to be a less than omnipotent or, like George W. Bush, fall victim to their own romantic notions of American power.

“This is what will end up defining this era of the presidency — the diminished power, the diminished authority, the diminished capacity to shape events,” says Robert Dallek, the presidential biographer. “It’s the presidency in eclipse.”