Blackmail is a demand for something from someone by threatening to accuse that person of a crime or immoral conduct that would tend to disgrace him or her. It does not matter if the accusation was truthful or not, or whether the accusation was later made or not. It helps the criminal, however, provided that the blackmailee thinks there might be something to the accusation.
There are many federal and state laws prohibiting blackmail. For example, 18 U.S.C. § 875(d) states that:
For example, Autumn Jackson was sentenced to 26 months in jail to be followed by 3 years supervised release for threatening to embarrass Bill Cosby in order to obtain money from him.[1]