You asked, “why did 20% of white evangelicals vote for Obama? why would evangelicals vote Democrat?”
That is like asking “why did the Corinthians think of men above that which is written?” (1Cor. 4:6)
You mean, “Why did 20% of Born again Evans vote like twice as many white Catholics?,” and why did only a 10% majority of even white Catholics vote like 70% of Evans?
I am not sure what your reasoning is supposed to prove, but it appears you are attempting damage control
by resorting to invoking the minority of Born again Evans who voted liberal like in in order to minimize that only 48% of Catholics voted for Romney, and just 59% white Catholics did, versus 69% of BA Evans and 57% of Prots overall. - , http://www.pewforum.org/Politics-and-Elections/How-the-Faithful-Voted-2012-Preliminary-Exit-Poll-Analysis.aspx
There simply is no debate that evangelicals are more conservative (though as foretold [2Thes. 2:3], this is in decline), and that only a minority of Evans voted like Catholics usually do, and are contrary to their profession, or that while conservative RCs voted for Romney, yet overall those whom Rome counts and treats as members in life and in death are liberal: http://www.peacebyjesus.com/RC-Stats_vs._Evang.html
your posts are accusative yet not giving a response for why evangelicals, white evangelicals with no historical baggage of Democrats vote for them -- do you have any reason for why evangelicals voted for OBama?