Matthew Yglesias has an interesting piece in TAP about the lackluster history of generals who became president. He focuses on a long-ago period, however:
Between 1840 and 1888, eight of 13 presidential elections were won by former generals, and several losing nominees had similar military backgrounds.
He then details the careers of the general-presidents during that era and finds only Ulysses Grant (with an asterisk) and Zack Taylor being any good. Of course, the entire nature of the presidency has changed since then–as has the military profession. Indeed, of the winners during 1840-88 period, only Grant was a professional soldier in anything close to the modern sense; the remainder were politician-generals of state militias.
One of the problems with the study of American politics, especially the presidency, is the “small N” problem: There are simply too few cases to draw useful conclusions. There have been only 42 holders of the office of president (Cleveland was both the 22nd and 24th president, making Bush number 43). That’s a pretty small sample to begin with. Factor in that the first several presidents weren’t the result of popular election; that, with the exception of a couple of wartime presidents, the office was radically less powerful pre-FDR; and the radical changes imposed by television, it’s arguable that comparison of modern presidents with those before Kennedy are highly problematic. This doesn’t make historical comparison uninteresting; it just means we need to take them somewhat lightly.