The key traits of an effective president are expertise in understanding presidential power, a desire to have power, and the grace to deal with the failures and frustrations in attempting to use that power. To get the first requires many years of political experience (although that alone doesn't necessarily suffice), which is why the presidency is no place for amateurs.
The American political system works best when the president is adept and vigorous in pursuing power. In the first place, other actors are depend upon the president to provide initiatives for them to support or oppose. But there is also a correlation between preserving presidential power and pursuing viable public policy. A president's contacts and the pressures he is subjected to give an unmatched insight into the conflicting demands that constrain policy. His efforts to navigate those pressures in a way that does not compromise his power, if done with expertise, tend to lead him to policies that (1) are forward looking, (2) are acceptable to all the stakeholders, and (3) are well timed.
The Sixties seem unlikely to throw up the kind of productive crises that FDR had to work with in the 1930s and 1940s -- the Depression and the Second World War. These crises increased the influence of the president within the political system without destroying it altogether. Neustadt contends that the potential destructiveness of war has priced it out of the market for productive crises. (I think that this understates the usefulness of limited wars for presidential influence.) The president will still face a discontinuity of constituencies with Congress even in the unlikely case of having partisan colleagues in control. Key sources of political conflict Neustadt projects for the Sixties (1) the size and scope of public spending, (2) the influence of the agricultural sector, (3) the influence of labor, and (4) racial integration. All of these will have disparate impacts on local constituencies, which means the president will need to rely on ad hoc Congressional coalitions for support.
Neustadt concludes by (implausibly) contending that the American system is not unique after all -- that other nations face a similar predicament of a single leader who must deal with disparate constituencies (even in parliamentary systems).
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