The problem is (and I know this is oversimplification), they've elevated 'stupid' to a virtue --for voters, not necessarily candidates. They label the belief that all parents should be able to send their kids to college as 'elitist', they tell people there's something wrong with making health care affordable to everyone, that taxes are unnecessary and evil, they invoke people's fear of differences so Obama STILL might be a Muslim, STILL might not really have been born in the US, and if he was born in Hawaii, that's STILL not in the US--and the list of things is nearly endless--
and they have SO pandered to stupid people because they LIKE sheep, and stupid people raise more stupid people because education is, after all, elitist, that this is where we are now.

This is the grown-up generation of Jerry Springer-watching people who've jumped on whatever conspiracy theory fad is being reported by owned talking heads giving them the 'news', that people seldom think for themselves and actually question what they're being fed. So even the ones who might possibly be able to think have knee-jerk reactions and close ranks against the enemies of stupidity and falsehood.

It isn't that difficult to see through lies, but you have to look, and the people who do are not the ones who are likely to believe it in the first place.