Apostate

[Sarah]

One who, after having received sacred orders, renounces hisclerical profession.

[Sarah]

One who has abandoned one's religious faith, a political party, one's principles, or a cause.

[Donald Trump]

In the Jehovah’s Witness ([JW]) religion:
Any baptized JW who openly disagrees with or [speaks out] against either the JW religion or the [Watchtower] Bible and Tract Society (WTBTS).
Apostates are considered dangerous “followers of Satan” and are therefore shunned.

[Luis Fok]

A person who renounces a religious or political belief or principle.

[Little_Girl]

someone who has given up their religion or left a political party