Alma 30

Having the witness of the Holy Ghost, Alma said to Korihor -

"...I know that thou believest, but thou art possessed with a lying spirit, and ye have put off the Spirit of God that it may have no place in you; but the devil has power over you, and he doth carry you about, working devices that he may destroy the children of God." (Book of Mormon | Alma 30:42)

I believe that this is the downfall of so many good men, especially in politics (possessed with a lying spirit)for political gain. Now days, that is almost expected. No one seem alarmed with outright lies and deception anymore. It can easily be brushed off as "I misspoke"..."its politics".

Later after being caught in his tracks, Korihor confesses -

"...I always knew that there was a God.
53 But behold, the devil hath deceived me; for he appeared unto me in the form of an angel, and said unto me: Go and reclaim this people, for they have all gone astray after an unknown God. And he said unto me: There is no God; yea, and he taught me that which I should say. And I have taught his words; and I taught them because they were pleasing unto the carnal mind; and I taught them, even until I had much success, insomuch that I verily believed that they were true..." (Book of Mormon | Alma 30:52 - 53)

A great truth is taught of those with a "lying spirit". The eventually begin to believe in themselves that they are true.