In 2008, pretty much anyone who wasn't a Republican and who had a pulse was going to win. Obama had a strong mandate for change based on the Republican Party having lost all credibility on both foreign and economic affairs. He got a lot of people excited about "hope" despite the fact that his actual policy schemes were incredibly centrist and corporate. He was very much a Wall Street candidate who managed to brand himself in the right way at the right time, and ride a wave of youth distaste with the present state of politics.
In 2012, I think that the Tea Party hit the wall of the four-year election. Democratic voter turnout increases in presidential elections because there's a direct correlation with higher turnout and a more liberal turnout. I think that Obama's apparent failure to get much done over two years helped the Tea Party immeasurably (and while I think no President could have repaired the Great Recession rapidly I do believe Obama made a number of mistakes and also showed the very limited nature of his progressivism during that time). But two years with the Tea Party showed people that they weren't a silver bullet either.
Even in 2016, I think you're going to see the same pattern. People are getting increasingly hopeless, and the first party that can actually make a real impact on people's perceived prosperity will have won a lot of the American electorate for a very long time.