After a few terms, maybe less, people will start to blame the current administration for all their problems, real or imagined, then they vote for the opposition because they're advocating change, a new kind of politics, schools, roads, all that good shit.
Then it happens all over again with the new party.
As to when it will actually happen, I don't pay enough attention to the polls or America in general to have any coherent idea, but it seems that the left over hate for the last administration will last at least 2 terms, although who knows how bad the economy is going to go down the shitter, so maybe people will blame Obama/Democrats if shit gets bad fast enough.
Of course, depending on when it happens, the current administration can always blame all the problems on the last one, and vice versa.