I would say it did hurt Obama, with "hurt" being a relative term. No it didn't stop him from winning, but one could easily make the argument that if the democratic party wasn't so divided and such, Obama would have won by a major landslide. Obama won, but not by much even after having a Republican President for 8 years that got the country in a mess. The truth is on that basis McCain never had much of a chance in the first place. The fact that the democrats were divided made Obama weaker, but not so much weaker that he couldn't beat McCain.
In this election, Obama is not as solid as a candidate as he was last. America has already had him as a President for 4 years and a lot of people disapprove of how he's handling things. (I'm not one of them though)
In fact, it was even said at one point that according to a poll (I think it was CNN) a generic republican vs Obama held today (although this was several months ago), the generic republican would win.
However, as to all the specific republicans running against Obama? (Paul, Santorum, Romney, Gingrich) Obama is beating all of them. The Republicans are killing each other. Period.