It is common not only to overestimate the influence that the president has on public opinion and policy, but to overestimate the influence the president has on even the decisions that he does make.And remember, Dickinson's example about Executive Office of the Presidency reorganization is in some ways an extreme case: the president really does have very broad authority within the White House, and the people who work there have no dual loyalties to Congress, or to long-term civil servants (as do cabinet secretaries and other presidential appointees in the executive branch).
Indeed, it may be worse for Barack Obama than it was for Jimmy Carter. There's no one in Obama's White House, at least not at the senior levels, whose career is as tied to Obama as Hamilton Jordan's was to Jimmy Carter. Virtually all of Carter's top White House staff were long-time Carter loyalists, and few had similar ties to the Democratic Party or to interest groups. That was generally true for presidents from Kennedy through Carter. These days, a more typical White House staffer would be Rahm Emanuel or, perhaps, Rob Nabors -- people who have worked for a succession of different politicians from their party, often with White House experience from a previous administration. Institutionally, the White House staff is still loyal to only the president, but personally Obama's White House staff is likely to have a strong loyalty to the Democratic Party (although, to be sure, working for a president will usually lead one to conflate the two).