His last book delved into 2,400-year-old material, but Paul Johnson’s latest Forbes column looks ahead to November.

Johnson identifies “certain simple yet definite characteristics” common to successful presidents — decisiveness, the ability to convey reassurance to voters, and at least one other trait.

[A] President must possess two or three core beliefs that center on the nature and limits of government—what it ought to do, must do and should avoid doing. In an ideal world government would do only three things—and those because no one else can: run external defense, keep internal order and manage an honest currency. In the real world, however, government must perform many other duties. Yet the more it takes on, the less likely it will perform the three essentials adequately. A good President remembers this always. …

… What Americans ought to be looking for in Obama’s replacement is someone who can redefine, in contemporary terms, what the essential features of the American system at its best are.