They are lost and lashing out at reality itself. The base of the Party is to be pitied more than feared. They have literally been conditioned to fear their own brains. Their religious indoctrination has actually destroyed their ability to reason. They literally believe this alternative reality that is far too extreme for even the extreme and it is scary!
"How on earth could they believe (fill-in-the-blank): that global warming is not real, that evolution never happened, that an embryo is a "person," that the right to carry a gun equals "security," that President Obama is a socialist, communist, Muslim, the Antichrist, soft on terror, a dangerous man, not a Christian, the wrong sort of Christian or that history text books should reflect America's "Christian country" status... Moreover, how could they really believe that Santorum could ever become president!
First of all the backbone of the Republican Party is the American Evangelical community and the conservative Roman Catholic community - Zealots. Secondly, the American Evangelicals and conservative Roman Catholics are raised from birth to reject common sense, learning and progress in favor of a literal interpretation of the Bible.
Having said that if your base is a group that has been trained to reject truth in favor of faith in faith. They will believe anything because rejection of what "everyone else believes" is a bedrock article of faith and your very identity. Science has rendered a literal interpretation of any scripture, be it the Bible, Koran, whatever, as impossible. For many religious people this means that they have sought out deeper meanings in a spirituality that depends on a more intuitive sense of meaning and purpose than a slavish attempt to follow texts that have been simply disproven.
The rise of the religious right within religion is designed intentionally to isolate, indoctrinate and "protect" from challenging ideas. Fundamentalist leaders, be they conservative bishops or evangelical leaders, do this because actual true information is no longer helpful to the fundamentalist religious cause. So that cause becomes about controlling the minds of the faithful by cutting them off from other opinions.
Having circled the wagons and gone inward, the Republican Party now speak their own language, have their own culture, and they despise and fear the country they dwell in as virtual strangers. This is a self-imposed exile.
I am old enough to remember similar group like the Citizens Counsel, the Klan and a nut named Hitler, who were able to convince enough people to cause unthinkable devastation to millions to which in hindsight we ask "How could they believe this stuff? Of course, the question is asked after the damage is done! It takes training for years to reject reality.
And that's my Thought Provoking Perspective...