This is a very interesting question. I think there is a big gap between Sarah Palin and a historian of American history. However is is not clear how one generally declares a source to be authoritative. Is a graduate student enough? Untenured professor? Tenured professor? Tenured for X number of years? Obviously, there are cases where all of the recognized experts and neophytes agree. However, when it comes to issues of interpretation, there will likely be disagreement. For the time being, we just have to play it by ear.
Of course, the declaration of authoritative sources could be an area of research. I'll leave that to others.
The hardest part of climbing the ladder of success is getting through the crowd at the bottom.