As stated before: history shows that the party that holds the presidency after the second term typically loses it. I will also add that if dems, once again, run away from the accomplishments of Obama (like they did with clinton and again in 2012), the dems will lose again.
That's really true only on a superficial level and most losses by the incumbent party are explained by events that don't always pertain to Americans being sick of that party.
1952: Ended 5 consecutive terms between FDR and Truman. Something was bound to change.
1968: LBJ decided to not run again, and the "heir apparent" (RFK) was assassinated thus handing the presidency to Nixon.
1976: Watergate, Ford Pardon.
1992: Conservatives weren't too happy with Bush I so he lost votes to Ross perot and Republicans were losing popularity overall.
2000: Florida.
2008: Iraq War. Defecit, The Great Recession.
That being said, the republicans are almost single handedly destroying any chance they have of getting back in the White House. Only the dumbest and biggest of partisans can look at the Republican Party and say, "you know, they've got some good ideas, I could get behind them!". The Republican Party has zero ideas that haven't been proven to be failed policies and they have zero new ideas.
This.
This even creates another problem. Democrats think they're successful because they are the better party when in realty they owe their success to the failures of their adversaries.
The G.O.P. has been losing ground in presidential elections since 1992 and that trend is set to continue in 2016. The party is in a shambles because you have to somehow be crazy enough to win a primary but also be sane enough to win a general election.
The fact that conservatives think people like Ted Cruz, Ben Carson, or Rand Paul have a shot at winning a general election is proof that they live in an another world.
In the end the GOP election will come down to Bush. Hard line conservatives may not like him, but he's the only one who is relatively sober and he has the money and family connections associated with his name and they will need that to try and defeat Hillary.
But even then it's gonna be really tough for them to sell a Bush over a Clinton as the general public doesn't have very fond memories of Bush. So in a sense; his name is his greatest asset while also being his greatest burden.