From this extensive piece on Barack Obama and his presidency, James Fallows considers why presidents fail:

We judge presidents by the specific expectations they ask to be measured against: inspiration (Kennedy, Reagan, Obama), competence and experience (Eisenhower, the first George Bush), strategic cunning (Johnson, Nixon), integrity and personal probity (Carter), inclusiveness and empathy (Clinton), unshakable resolve (the second Bush). But eventually each is judged against his predecessors, a process that properly starts with a reminder that all begin their terms ill-equipped, in ways that hindsight tends to obscure.

The sobering realities of the modern White House are: All presidents are unsuited to office, and therefore all presidents fail in certain crucial aspects of the job. All betray their supporters and provoke bitter criticism from their own side at some point in their term. And all are mis-assessed while in office, for reasons that typically depend more on luck and historical accident than on factors within their control. These realities do not excuse Obama’s failings, but they do put his evolution in perspective.

Presidents fail because not to fail would require, in the age of modern communications and global responsibilities, a range of native talents and learned skills no real person has ever possessed. These include “smarts” in the normal sense—the analytical ability to cope with the stream of short- and long-term decisions that come at a president nonstop. (How serious is the latest provocation out of North Korea? What are the “out year” budget implications of a change in Medicaid repayment formulas?) A president needs rhetorical clarity and eloquence, so that he can explain to publics at home and around the world the intent behind his actions and—at least as important—so that everyone inside the administration understands his priorities clearly enough that he does not have to wade into every little policy fight to enforce his preferences.

A president needs empathy and emotional intelligence, so that he can prevail in political dealings with his own party and the opposition in Washington, and in face-to-face negotiations with foreign leaders, who otherwise will go away saying that this president is “weak” and that the country’s leadership role is suspect. He needs to be confident but not arrogant; open-minded but not a weather vane; resolute but still adaptable; historically minded but highly alert to the present; visionary but practical; personally disciplined but not a prig or martinet. He should be physically fit, disease-resistant, and capable of being fully alert at a moment’s notice when the phone rings at 3 a.m.—yet also able to sleep each night, despite unremitting tension and without chemical aids.

Regardless of your political stance, I suggest setting aside an hour to read this piece by James Fallows.