In The Week, Damon Linker has a column arguing that presidential elections in America are no longer principally about the respective policies that each party stands for. Rather, elections have become about "culture, identity, signaling, and symbolism" — voters gravitate toward candidates who best reflect their tribal values, and stick with them.
In New York, Jonathan Chait has some data that underscores this point. The mythic American swing voter who can be swayed by argument and circumstance has, for all intents and purposes, disappeared. Elections are increasingly decided by sheer partisanship, and, in his words, "negative partisanship" — meaning voters will go to the polls to prevent their cultural enemies from taking power.
[Recent election data] suggests that the electorate is much less fluid than it used to be, and is more easily understood as hardened blocs defined by shared cultural identity (or shared mutual cultural antipathy). [New York]
What does this mean for 2016? It means the tribe with the most voters and the best turnout has the advantage. For now, that would be the Democratic Party, which means Hillary Clinton may very well go on to victory despite factors that may have hurt a candidate in her shoes in the past, such as middling approval ratings for the incumbent president.