I guess Menendez is party neutered but it is good of the AP to identify the political parties of those that asked for an investigation.
Since an arrest warrant is a command by the court to bring before it, without undo delay, a person named it would seem to me anyone who interfered with that command would be in violation of a court order or had obstructed a court activity. They should be so indicted if a violation of a criminal law or if not they should be arrested for contempt. Either or but the result should be the same: Jail time.