Imagine having a brain that disables its own skepticism and vigilance circuits. That is what some religious people have:

Brain shuts off in response to healer’s prayer

The basic set up is to take a group of rational people and a group of devout believers. You play recorded prayers for both groups, and tell the groups that some of the prayers are being spoken by someone “possessing divine healing powers”, while the others are being read by those less endowed. In fact, there is no difference in the people reading the prayers. The result:

Only in the devout volunteers did the brain activity monitored by the researchers change in response to the prayers. Parts of the prefrontal and anterior cingulate cortices, which play key roles in vigilance and scepticism when judging the truth and importance of what people say, were deactivated when the subjects listened to a supposed healer.

Conclusion: if you have a group of devout believers, their leader can say anything and they will believe it, because they have deactivated the part of the brain that would catch lies an nonsense.

Does this same effect apply to Rush Limbaugh? That would explain a lot.