There is a must-read review of past American Presidents' "experience" as it relates to their perceived quality of governing at http://www.electoral-vote.com/ .
How good Are experienced presidents, anyway? Suppose you had to choose between two Presidential candidates, one of whom had spent 20 years in Congress plus had considerable other relevant experience and the other of whom had about half a dozen years in the Illinois state legislature and 2 years in Congress. Which one do you think would make a better President? If you chose #1, congratulations, you picked James Buchanan over Abraham Lincoln. Your pick disagrees with that of most historians, who see Lincoln as the greatest President ever and Buchanan as the second worst ever, better only than Warren "Teapot Dome" Harding. Both served in what was probably the most difficult period in American history, where slavery and secession tore the nation asunder.
More after the jump...
Before becoming President, Buchanan had served 6 years in the Pennsylvania state legislature, 10 years in the U.S. House of Representatives, 4 years as ambassador to Russia, 10 years in the Senate, 4 years as Secretary of State, and 4 years as Ambassador to England. Talk about experience, Buchanan did just about everything except serve on the Supreme Court, a job he was offered by President Polk and refused. Yet by any measure, he wasn't up to the job as President. In contrast, Abraham Lincoln served 8 years in the Illinois legislature and one term in the U.S. House (1847-1849), a decade before becoming President. The rest of the time he was a lawyer in private practice, a bit thin one might say.
Click here for a chart that summarizes the results of their review. The Presidents in the lower left are high-quality Presidents with little experience. The Presidents in the top right are poor-quality Presidents with tons of experience.
Note that there are a lot more Presidents in the bottom left than the top right