My best guess: 50-60% of All Republican voters are christian evangelicals.
With gay marriage being resolved by the supreme court a lot of them will dropout of voting in 2016 since one of their top wedge issues are gone.
I highly doubt that. Abortion was supposedly resolved as a political issue by the Supreme Court over 40 years ago and there is still (likely mostly unconstitutional) legislation being passed on it seemingly weekly and it's still a big issue for many voters.
To be sure, gay marriage is no where near as complex an issue as abortion, but gay rights in general is in many ways, and this one ruling doesn't begin to settle all the issues around gay rights.
