Model Rule 8.4, which is the basis of Rule 8.4 in most, if not all states, holds that it is professional misconduct for a lawyer to "violate or attempt to violate" the Rules of Professional Conduct. Yet, you rarely see cases imposing discipline for an attempted violation of the rules.
This makes Lawyer Disciplinary Board v. Sayre interesting. In this case, the Virginia Supreme Court imposed discipline on an attorney for a number of offenses and one of them involved an attempt to violate the rule against sex with clients. The lawyer admitted that he knowingly engaged in inappropriate and sexually suggestive communications with the intent of initiating a sexual relationship with a client. Because his attempt was unsuccessful, the Court ruled the conduct was not a violation of rule 1.8, but it was a violation of rule 8.4.
The Legal Profession blog has a summary here.