Obama was the weakest candidate in 2008, look how that turned out for him.
Weak? He is a personable, slick campaigner. He consistently got his message across. He learned from his mistakes (like his "guns and religion" gaffe).
Perhaps instead of weak, we should say he was the most electorally disadvantaged? We have to separate his strong political and intellectual skills from the profile which, if you described to people without seeing the man in person, would have had you write him off as a candidate for President.