Obama has at the very least stabilized this country, but republicans can draw off of white privilege as a justification for their resume. All they have done in 5 years is relentlessly hit Obama with substance-free attacks, and in conjunction offered zero solutions, with the added touch of controlling the least productive house in united states history.
Republicans are gonna be Republicans, and they decided a long time ago not to cooperate with Obama on anything, but to be honest I think a lot of this is the Obama Administration's own fault, what with the unnecessarily crappy rollout of Obamacare.
After the whole "shutting down the government" thing, the midterms should've been a gimme for Dems. All they had to do was make sure the damn website worked before launch and make up their minds one way or another about the "you can keep your insurance plan" things. So they kind of screwed themselves over.
In any case, there's a good chance the GOP takes back the Senate this year, but even so, 2016 will still be shytty for them. No only will Hillary probably win, but the GOP will likely lose the Senate back (if they get it this year) and lose House seats. Of course, this is all speculative but that's what seems likely to happen at this point.