What is relevant is that Christianity enjoys an excellent reputation in the US. So much that refusal to cater to Christianity is a political death-sentence. (The US will have a gay President long before it has an atheist President.)
The Republicans proclaim to be Christians, taking advantage of the reputation. Not only that, they also use arguments derived from christian teachings for political purposes. And all the while they not only exhibit indifference to Christianity, they actively break the rules it has laid out.
If Republicans voiced their political opinions without the cover of a hijacked christian mantle, they would be toast. But all the extremist Christians care about is that the candidate claims that he's Christian.
The candidate has been divorced?
Lies?
Has had an affair?
Treats poor people badly?
Amasses wealth instead of donating it?
Refuses to pay his share to society?
Is vengeful?
Nobody cares. You can commit the worst atrocities, but if you call yourself a Christian, the voters will will-fully close both eyes to overlook that. Because Christians are defined as the good guys in the US.
"Of course he will make America great again! It says so on his hat!" - actual quote from a Teabagger
"My favorite book is the Bible!" - "Do you have a favorite part of it?" - "All of them!" - paraphrased quote from Donald Trump
What do you think why the extremist Christians in the US support the un-christian heathens the GOP has put forth as candidates?
What if Donald Trump had said: "Meh, I'm not that much into religion. Haven't been in a church in years. I prefer to go golfing on Sundays." ?
It's okay to hate people and worship Mammon, but don't you dare to have anything but praise for Christianity!