Peter Allan is a leading entertainment and intellectual property attorney in New York City. His writing has also appeared in the Huffington Post.

Successful business experience is the central rationale for former Gov. Mitt Romney's 2012 presidential campaign. To support Romney one must, at a basic level, believe that being good at business either generates experience or hones qualities that are likely to produce successful presidential leadership at a reasonably high rate. One assumes that the validity of this proposition is testable against the historical record. If Romney is correct, presidents with significant business experience should outperform those without—and this fact should be reflected in the presidential rankings that have been compiled by a bipartisan group of historians since 1948. If Romney is wrong, if business leaders perform as well or less well than the average, then business success is at best immaterial and may actually be detrimental to presidential leadership. In that case a core tenet of Romney's presidential candidacy evaporates.

We have had 20 presidents in the modern era (i.e., since 1900). Five of those had significant business careers before entering politics. Unfortunately for Romney, the results are not good for the businessmen.

None of the great or near-great presidents—Teddy Roosevelt, Franklin Roosevelt, Harry Truman, or Woodrow Wilson—was a businessman. Truman was a failed businessman (a haberdasher) before entering politics, but that hardly constitutes a ringing endorsement of Romney's claim for private sector ascendency.

For that matter, none of the better-than-average presidents was a businessman either. In this category think of Presidents John F. Kennedy, Dwight Eisenhower, Ronald Reagan, Lyndon Johnson, and Bill Clinton.

Probably the most successful president with real business experience (and success) was George H.W. Bush. Before going into politics he founded Zapata Petroleum, which ultimately became Pennzoil. Bush 41 ended up a one-term president unable to kick-start an economy in a recession and seemingly out of touch with the problems of the common man. Sound familiar?

It gets worse from here. Jimmy Carter, another one-term president beset with economic woes, was a success in agribusiness (peanut farming) before getting into politics. He generally falls into the lower half of the historians' rankings.

And then we get the big three—the men widely considered by historians to be the worst presidents of the modern era: Warren G. Harding, Herbert Hoover, and George W. Bush. One left the country on the verge of a depression, one left the country in a depression, and one presided over such corruption and ineptitude that despite the failings of the other two he still manages to get the lowest ranking of them all. And yet all three made millions of dollars in the private sector before entering politics. All three were successful businessmen (a newspaper publisher, a mining tycoon, and the owner of a professional baseball team). Bush 43 even went to Harvard business school, like Romney, and like Romney promised to bring business principles to the Oval Office.