Mitt Romney has said more than once that his private sector experience will help him reinvigorate America's stagnant economy.

The Republican nominee is so adamant about business acumen as a prerequisite to the presidency that he has pitched a constitutional amendment that would require presidents to have spent at least three years working at a for-profit company. But is business experience really an indication of presidential prowess?

Scott Shane, a professor of entrepreneurship at Case Western University, recently tried to answer that question in an Entrepreneur magazine column. Shane identified presidents with business experience and noted where they stacked up in a survey of 238 presidential scholars ranking the best and worst commanders in chief.

Six of the 10 "best" presidents had business experience, albeit some notable failures. One POTUS owned a general store, another started a clothing shop, but both businesses ultimately went bankrupt. Meanwhile, some of the "worst" presidents hit entrepreneurial home-runs, including a highly profitable newspaper and a family peanut farm that expanded into an international business.

"Among those presidents with business experience, the successful ones don’t appear to be better at running the U.S. than unsuccessful ones," Shane concluded.

To shed some more light on the issue, we've compiled the full list of past presidents who ran their own ventures. Do you think business experience should be a prerequisite for future presidents?

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  • Abraham Lincoln

    Apart from being the only U.S. President to receive a patent, Lincoln was also a <a href="http://www.usatoday.com/money/smallbusiness/columnist/abrams/2009-02-13-lincoln-advice_N.htm" target="_hplink">small business owner who faced his fair share of adversity</a>. In 1833, he opened a general store with partner William Berry, though that store would go out of business within a year with Lincoln's possessions seized by the sheriff. Lincoln went on to own a law practice and invent machinery to lift riverboats over sandbars, though the device was never produced. <strong>Presidential Ranking*:</strong> 3 *<em>Based on Siena Research Institute's <a href="http://www.siena.edu/uploadedfiles/home/parents_and_community/community_page/sri/independent_research/Presidents 2010 Rank by Category.pdf" target="_hplink">2010 survey</a> of 238 presidential scholars.</em>

  • Warren G. Harding

    <a href="http://www.history.com/topics/warren-g-harding" target="_hplink">Harding purchased a struggling newspaper</a> named <em>The Marion Star</em> when he was only 19. The highly profitable newspaper would eventually provide Harding with the income needed to fund his campaigns for public office in the coming decades. <strong>Presidential Ranking:</strong> #41

  • Franklin Delano Roosevelt

    FDR, who suffered from polio, <a href="http://suite101.com/article/franklin-roosevelt-and-hydrotherapy-a223441" target="_hplink">raised funds to turn a spa into a for-profit healing center for victims of polio</a>. It eventually became the Roosevelt Warm Springs Institute for Rehabiliation, which still stands today. <strong>Presidential Ranking:</strong> #1

  • Harry Truman

    After serving in World War I, <a href="http://www.trumanlibrary.org/hst-bio.htm" target="_hplink">Truman came home to Kansas City and opened a men's clothing store</a> with wartime friend Eddie Jacobson. The store was open from 1919 to 1922, but eventually fell victim to the post-war recession. Narrowly avoiding bankruptcy, Truman eventually paid off all his debts. <strong>Presidential Ranking:</strong> #9

  • Jimmy Carter

    Carter left the Navy in 1953 to <a href="http://www.nps.gov/nr/travel/presidents/jimmy_carter_nhs.html" target="_hplink">take over the family peanut farming business</a>. He eventually expanded the Golden Peanut Company into an international business with warehouses and a peanut-shelling plant. <strong>Presidential Ranking:</strong> #32

  • George H.W. Bush

    In 1951, the <a href="http://www.senate.gov/artandhistory/history/common/generic/VP_George_Bush.htm" target="_hplink">elder Bush started the Bush-Overby Oil Development company.</a> By 1953, Bush-Overby would merge with Zapata Petroleum Corportation, a venture that later made him a millionaire. <strong>Presidential Ranking: </strong> #22

  • George W. Bush

    George W. Bush, the first U.S. president with an MBA, <a href="http://www.wsws.org/articles/2002/aug2002/bush-a01.shtml" target="_hplink">invested $600,000 in the MLB's Texas Rangers</a>. He later sold his stake in the team for a cool $15 million. <strong>Presidential Ranking: </strong> #39

  • Herbert Hoover

    Hoover got the idea for a mining company after studying geology at Stanford University. In 1908, he <a href="http://www.u-s-history.com/pages/h1580.html" target="_hplink">started his own engineering business</a> that helped find investors for developing mines. At its peak, the firm employed 175,000 workers worldwide. <strong>Presidential Ranking: </strong> #36