Obama was really good at letting people project what they wanted on to him politically, while still broadly holding to the neoliberal agenda, and lots of people were insanely naïve at the time. I mean, you had people who claimed to actually expect the election of Obama to usher in a post-racial epoch in the USA, as though all the racists were going to say, "Aw, shucks, the black guy won? Well, hang it up boys, we have to face reality and accept we've been wrong all along."

He also benefitted from pretty excellent political cover from criticism, where, like many vocal Biden supporters are doing right now, any criticism of him would be associated with outright support of the vilest opinions espoused by the GOP at the time. If you said "You know, this Obama guy isn't as great as he's being made out to be," you'd have people assuming you were some nutjob that thought he was secretly Kenyan, or whatever other crazy conspiracies the Tea Party folks trotted out. I don't think it was purely malicious or cynical attempts to discredit people all the time, but there was a big chunk of people who wanted to believe in their conception of Obama, which couldn't admit that he wasn't the savior sent from on high to resolve all the country's problems in exactly the manner they had hoped he would.