Most Republicans think their side is mostly losing in the political process, and most Democrats also think their side is mostly losing in the political process.I suppose this is partly because people are focused on different things. Many Democrats care most about economic inequality, which is getting worse by the day. Many Republicans are focused on issues of public morality (e.g., gay rights) where Democrats really are winning. The Obama era has been a political mixed bag, so there is something for everyone to hate.
But mainly I just think that the mood in the country is sour.