instead of saying that I say that politicians do not commit errors, I would prefer to be more explicit:
When you discuss with contents, contents are always true or false, and you are “allowed” to discuss with them, and say, for instance, that he is wrong in this or that.
However, when you look at the other side of the political discourse, its form, the discourse is neither true nor false, neither an error not a right opinion, etc. And you look, instead, for the practical meaning. You ask for what purpose such declaration was made? What are the results in the context of such declarations. Those are two totally different questions.
And, since politics is a goal-oriented discourse, it is a discourse intended to the form by means of the content, while people hear contents and believe that the speaker indeed attempts to them, not to the mobilization of your mind.