There are (at least) two types of liar. Those who consciously tell a blatant untruth, and those who...somehow... like a good actor who becomes his character for the duration of the play, manages to lie to himself in order to advance a position.

Since we don't read minds, it is hard to guess exactly what processes are going on in the heads of folks like Romney who can seemingly hold 2 or 3 contradictory positions at once... or at least on successive days. It may be that Romney actually convinces HIMSELF that he's merely 'clarifying' a point or position.
   In any case, the degree to which he does it, in the face of bushels of evidence about his weather-vane-etch-a-sketch behavior, should be a red flag to voters.... but, as noted, those who already WANT to believe what he spouts will just suck it down....