I understand conspiracy stuff is frowned on here (though semi-secret power rotation agreements between political parties recur often in Latin America), but in terms of outcomes, Shevek is on to something.
Since the 22nd Amendment to the US Constitution was passed, imposing term limits on the presidency, with the big exception of the 1977-93 period, the White House has switched between the Democratic and Republican parties every eighth year almost like clockwork. The exception was the one Carter term, followed by three Republican terms. The normal pattern would have been the switch between parties occurring in 1984.
Note that this was definitely not the case before the 22nd Amendment, when long periods of the White House being in control of one party was the norm. In fact, between 1861 and 1933, there were Democrats in the White House for only four terms, or sixteen years. Then you had the five terms of Roosevelt -Truman.
Another thing that happens pretty consistently, and this goes back to when states started allowing their electorates to vote for presidential electors, that in the election eight years after a party gains control of the White House, its popular vote percentage margin shrinks compared with four years earlier. This is a weird statistic, but surprisingly consistent. There are only three exceptions, 1892, 1896, and 1904. The 1892 and 1896 exceptions are partly explained by the circumstances of 1888, when the voters wanted to re-elect Cleveland but he lost in the electoral college, the voters made sure he was elected in 1892 then deserted the Democrats.
This can be explained by voter fatigue after eight years, similar to the "six year itch" tradition of Congressional losses in the sixth year of an administration.
But for whatever reason, the 2012 Republican primary field of contestants was fairly weak as these things go. It was definitely much weaker than in 2016, and I wold argue that it was weaker than in 2008 or 2000.