One one think running unopposed would pretty much guarantee a victory.  But in Obama's case, not completely.

If you're scratching your head,  Obama still has to run in "primaries."  There are still Democratic caucuses even though he is the incumbent, and the Dems do not plan to put someone up against him in November.  In Oklahoma, Obama was running technically unopposed, but still lost in 15 counties. Operation Rescue founder Randall Terry actually beat the Prez in those areas, and Obama only got 57 percent of the vote.  Terry got 18 percent of the 43 percent of the votes that did not go to Obama. Three other candidates split the remaining 25 percent.