In an interview with Mother Jones, Sasha Issenberg explains how data analytics is redefining how campaigns understand voters. What doesn't work:
One thing is how little the traditional messaging around "Do your civic duty," "Your vote matters,' all this sort of League of Women Voters stuff—how little impact that has had in test after test of getting people to change their behavior. In test after test, making voting seem dutiful and being part of this very responsible minority and "Don't be part of the problem," turns out not to work. That was such standard form of messaging that you would hear on the weekend before Election Day.
What we don't know:
A lot of the big stuff is still a total mystery to us. We still have very little idea what ads do; we still have very little idea what a convention does; we still have very little idea what a vice presidential pick does; we have very little idea how broad messaging stuff affects a race. There's tons of uncertainty about that, and the smartest people are more uncertain than the dumbest people about it. The more you know the less confidence you should have that any of that stuff is explainable and predictable.