No, he isn't finished, yes it's very hard for him at this point.
Even with approval ratings in the basement, he still leads or matches all his Republican challengers. That's probably a reflection on the quality of those candidates more than anything.
The Republican party itself is also extraordinarily unpopular, recording it's worst ever unfavorables, and congress approval at an all time low. Despite everything, Obama remains in the top tier of popularity among politicians in Washington atm.
If Obama wins, it will be in the mold of Harry Truman in 1948, who despite being very unpopular himself, convinced people that the Republicans, having just regained congress 2 years earlier after 18 years of wilderness, would be even worse. Truman not only won that election, but swept Democrats back into control of congress, which they remained in control of for the next 46 years