The Rule of Thirds is a concept in photography that helps to guide one to good composition. In politics, however, I think it can be shown in a different way.
In the general population, it seems that no matter what happens in the real world, you have about a third of people that will back the Republicans. You also have about a third that will back the Democrats, regardless of what is going on.
It's the final third, that slice that is often described as "undecided" that will ultimately determine which way a national election will go. You may call them undecided, a recent term that's been used more lately is the "low information" voter. These folks are mostly apolitical, and have very little interest in elections, by and large. This group is often swayed by the economy, voting with an incumbent if the economy is on an upswing, or against when the economy tanks, as in a recession. Timing is everything.
Think about that as we approach the 2016 election. Forget the smoke and mirrors about marriage equality, Planned Parenthood, Iran and Iraq. Those issues don't win elections. For the key to the 2016 Presidential election, look to the jobs and economic numbers, and closely observe the people that have no idea what is going on in the world. They have the key to the direction this country will be heading toward.
Ah yes. The American Experiment.