Changing your mind is not the same as being a "corrupt liar". It was Comey's job to follow the law, and he didn't do that.
This isn't changing your mind like choosing mustard over mayo on your burger. He made the case criminal acts took place and after he took that oath, it is his legal duty to follow through on that. Article 2, Section 3.
Also, isn't that just a cop-out that he changed his mind? It seems that can and is an excuse for almost every promise he abandons. 'Oh, he just changed his mind...' In the past, any candidate who 'changed his mind' on campaign promises was considered, rightfully so, a corrupt liar.