In a chapter entitled "Why Great Men Are Not Chosen Presidents" in his book The American Commonwealth Viscount Bryce explores this question at some length:
Europeans often ask, and Americans do not always explain, how it happens that this great office, the greatest in the world, unless we except the papacy, to which anyone can rise by his own merits, is not more frequently filled by great and striking men. In America, which is beyond all other countries the country of a “career open to talents,” a country, moreover, in which political life is unusually keen and political ambition widely diffused, it might be expected that the highest place would always be won by a man of brilliant gifts. But from the time when the heroes of the Revolution died out with Jefferson and Adams and Madison, no person except General Grant, had, down till the end of last century, reached the chair whose name would have been remembered had he not been president, and no president except Abraham Lincoln had displayed rare or striking qualities in the chair. Who now knows or cares to know anything about the personality of James K. Polk or Franklin Pierce? The only thing remarkable about them is that being so commonplace they should have climbed so high.
About this Quotation:
In this quotation James Bryce asks a question which others have also asked, in particular the Nobel Prize winning Austrian economist Friedrich Hayek: namely, “Why the Worst Get on Top”, in his book The Road to Serfdom (1944). Here Bryce, writing some 64 years before Hayek, reflects on the quality of the men who rise to the top position in American politics.