This is bunk. A lot of people, especially conservatives, believe this; but it is almost certainly factually wrong and thus a huge insult to Obama. Academics who have studied the election closely believe the race was about two or three points *closer *than it would have been had there been a generic white male Democratic nominee. It was just a very bad year for Republicans to begin with, then the economic collapse and McCain’s response to it was poor, and Palin dragged down the ticket further.
Although I love Obama (and my fondness has not lessened one bit over the past four years BTW), this also implies that Democrats were lucky it was such a wave election, as they took a big risk nominating a young, inexperienced black ivory tower academic type who had ties to radicals and had a name that Jon Stewart memorably likened to “Gaydolf Titler”.
It’s also true that–again contrary to the conventional wisdom, but per the research of political scientists–a generic white guy would likely be more comfortably leading in the race for reelection given the same record and economic trends.