Why can't most Christians understand the need for separation of religion and govt?

[Mystical]

According to the numbers, the only denomination that's gaining members in the US are the evangelicals.  And they take a dim view of more moderate denominations, like Catholicism.

Regarding the presidential candidates, the Republicans have always been split between the money people (business interests, military industrial complex, prison industry) and the religious people.  Now, their interests intersect quite often, but the money people are smart enough to know that too much lunacy is bad for business.  God's nice and all, but money is real.  The problem is that the religious people took over the Tea Party.

A lot of people don't remember this, but the Tea Party started off as a libertarian astroturf movement by the Pauls and their allies to protest what they saw as government overreach with taxes in general and the bank bailouts in particular.  It was quickly co-opted by lunatic Christian conservatives, and they now basically exist only to try to make things like they were ~2000 years ago because they think biblical times were the bee's knees and the Federal government is evil by definition.

The Tea Party holds a disproportionate amount of power in the GOP.  They're shrill and militant, and their followers vote, period.  So, during this pre-primary phase, every conservative candidate pulls hard right in an attempt to appease the wackos.  And it generally backfires, because the majority of the country isn't like that, so the Republican candidate must attempt to move back towards the center, but in doing so, they appear disingenuous to both sides.  

It's hard to walk away from crazy.  The moderates think you're actually crazy and are trying to appear sane while the crazy think you were never crazy to begin with.  Mitt Romney is a classic example.  Yeah, he's Mormon, but he's fairly liberal compared to the Tea Party people.  His clumsy attempt to be all things to all people backfired.

This is the best answer I got I think.. Very helpful, thank you for helping me to understand. :
When I was in high school (in Kansas), our government teacher helped all of us register to vote after showing us political videos of the republican candidates. The year was 2004. The democrats weren't mentioned much lol.
At the time (and I cringe now at the thought), I chose Huckabee to be my favorite and of course I registered as a Republican! I think I'm still registered there as such since I haven't voted in. Kansas since. This upcoming election terrifies me, to be honest. Mainly because of how well the republicans can blame shift. For example the governor of Kansas pretty much bankrupt the state with his "no taxes for business will trickle down a miracle" plan. I heard this idea started with Rush Limbaugh and the mindset that taxes killed Jesus somehow. Anyone remember what thAt was all about? I was quite too ill at the time to bother with politics. If Brownback hadn't been able to ss d 1steal Obamas bailout money set aside for the elderly to pay for their medicines and such to balance his huge hole in the budget.. Anyways long story short Kansans are suffering. Workers were laid off in the tens of thousands so the employers could pocket the money, utility companies quadrupled their price one month with no warning, Even the WIC program was cut and sent over to be a privately church sponsored program! Imagine being a single mother with a baby and having to go to a snobby church just to get milk and cereal supplements -- or worse, childcare!But anyone I'd ask (mostly foreigner taxi drivers, small town church goers, and students at my apartments) when I was living there last year would quickly blame Obama for everything. Since I've moved away they actually re elected Brownback as governor! This, is frightening to me. Anyone who openly or secretly endorses their religion as being superior to the rules set in place that they are supposed to follow and uphold --scares the living daylights out of me!