One main reason why Barak Hussein Obama will not win the Presidency: he's a not-quite-one-term Senator:
(1) He has no executive experience, neither as a Governor nor as a cabinet officer nor as a general.
(2) He also lacks any serious experience dealing with issues of national importance, as a distinguished junior senator for a mere four years.
(3) Beginning in 1964, senators are just 0-5 at winning the Presidency when they manage to get a major partisan nomination.
(4) Americans never have held a particularly favorable opinion of Congress, and they rightfully hold this particular deeply corrupted, bickering, odious class of clowns in particularly low esteem and even more loathe the Democrats among them. The American people simply see a group of odious obese obstructionists oblivious to national security but bereft of the leadership skills to do anything meaningful besides transferring tax dollars as kickbacks to bribing lobbyists.
It's historically even more ludicrous to assume that a Republican Senator (who never served as Governor) will ascend to the Presidency. No Party ever has nominated a Senator to succeed a two-term president. They always choose a senior administration official (vice-president, secretary of state, or another cabinet officer) or occasionally a Governor.
I agree with you in theory, but Warren G. Harding and John F. Kennedy, the only two men who I believe directly made the jump from Senator to President succeeded two-term Presidents of the opposite party - Woodrow Wilson and Dwight D. Eisenhower.