Something similar has happened with global warming. It has become a conviction of much of the GOP that you and I, with our cars and factories and leaf blowers and barbecue pits, are off the hook — innocent of cooking the atmosphere. That being the case, it therefore is not the case that anything has to be done about it. Only much of science, common sense and your average walrus differ, but the GOP soldiers on. This is a version of Nancy Reagan’s pledge: Just say no.

Not every GOP candidate adheres to all of these cockamamie beliefs. Mitt Romney has not signed the antiabortion pledge (he has some quibbles), and in the Senate, Tom Coburn has broken with Norquist about raising revenue. But the net effect is to establish an intellectual barrier for admittance to the presidential race: Independent thinkers, stop right here! If you believe in global warming, revenue enhancement, stimulus programs, the occasional need for abortion or even the fabulist theories of the late Charles Darwin, then either stay home — or lie.

This intellectual rigidity has produced a GOP presidential field that’s a virtual political Jonestown. The Grand Old Party, so named when it really did evoke America, has so narrowed its base that it has become a political cult. It is a redoubt of certainty over reason and in itself significantly responsible for the government deficit that matters most: leadership. That we can’t borrow from China.