As a Catholic, I do not know exactly what evangelicals want or get -I would suspect they get more of what they want from the GOP than they would from the left...
And another -- Why does the GOP Keep promising what, you say, they can't deliver anyway?
Politics is all about making promises -identifying goals that align with and identify a principle based ideology... I do not say the GOP can not deliver goals; what I say is that delivery takes time, e.g. it took 40 years to get where we are on abortion -turning abortion around is not going to happen over night...
As such, it is about the direction and journey (principle) more than it is about a destination (goal) OTHERWISE a political party would cease to exist or change drastically when "goals" were met. e.g. we were not promised a war on terror; however, we got one AND we had a GOP idealogical response to it rather that whatever the left would have done... AGAIN, principles -direction...
So what it comes down to as far as realistic support is political support of principles -support of principles AND staying the course regardless the day to day or year to year ups and downs with regard to goals...
Politics is also dealing the power you have, in order to get what you want. The only reason to be part of a political party, is to multiply the influence you have. Social conservatives, catholics AND evangelicals have elected this group of republicans. I think it's time to play.