It was humorous to see folks suggest that he might possibly win re-election.
People said the same about Walt Minnick. 
Democrats tend to be more partisan, from what I can tell. Minnick is conservative enough to be able to easily hold his district, while Cao is sunk more or less by virtue of the fact that he has an R next to his name.
I think racial voting has something to do with it as well. A liberal Republican probably has a reasonable shot of holding a white liberal Democratic district. (That said, Cao probably isn't liberal enough for his district anyway).
