why is all the opposition commentary about the caliber of republican candidate at the forefront?
It is fine to call out attributes needed to be a "worthy" candidate.

Does that rhetoric pre-suppose that an unacceptable incumbent cannot be out voted?

I personally think the disadvantage Obama has this time around is that he has become a known entity. As an emerging candidate in 2007 he won support with his eloquent speeches and myriad of promises.

However, as a known entity.....more talk than walk....he has turned being an incumbent into a liability.

Using the current measuring stick used on republican candidates, he would most certainly have been and is still unqualified as well.

btk