By Richard Sammon, Senior Associate Editor August 1, 2008 Barack Obama's largest problem may be overconfidence in coming weeks, even appearing unwittingly as if the election were a fait accompli. Tom Dewey had that problem in 1948 against Harry Truman, a plain spoken, unglamorous and unpopular underdog. Note to Obama: McCain may be reading up on that storied election.Obama is in a bit of a corner on the confidence factor. Appearing too confident will cause him to look like he is treating the election as a mere formality that is delaying his inauguration. And above all else, American voters don't like to feel taken for granted. But for a man whose opponent has made his experience and qualifications a chief issue, Obama also needs to display competence and the ability to walk surefootedly through a world filled with political, security and economic threats. Add these factors together in the overconfidence oven -- his largely successful European trip, his high-level statesman-like meetings with foreign heads of state, his Berlin speech to 200,000 and his recent talks with economic high-flyers. Plus the Obama-Rama Democratic convention where he will accept the nomination in an outdoor stadium amid a sea of adoring faithful. (One late night comic cracked recently that Obama has to do it in Denver because apparently Mount Sinai was booked that night.) He may smoothly strike the balance between arrogance and timidity, but he'll have to persuade voters from now until Election Day that he is still trying to sell them -- that he needs them more than they need him. Advertisement For an excellent account of the confidence problem that plagued Tom Dewey and how it may relate to Obama in modern times, check out elections expert Rhodes Cook in the Wall Street Journal.