The law doesn’t preclude them from representing a client unless they believe their services are being used to further a crime or harass others. The Supreme Court has provided broad coverage to the powers of a President acting in an official capacity.

It is up to each attorney individually to decide where their personal ethics do not align with their professional obligations but this is not an issue per the bar association’s professional rules of conduct. However, feel free to read through them and provide counter arguments based on their actual professional code.