WASHINGTON -- The Senate ethics committee has appointed a special counsel to investigate Sen. John Ensign, the Nevada Republican whose problems arose from an affair with a former campaign aide.

Carole Elder Bruce, who will conduct a preliminary inquiry, is a defense attorney in white collar criminal cases and a former federal prosecutor in Washington. She has been an independent counsel and has represented public figures in congressional investigations.

The Justice Department has dropped an investigation into whether Ensign conspired with the husband of the woman to violate federal lobbying restrictions.

A preliminary inquiry determines whether there's enough evidence to conduct a higher level review or whether the case should be dismissed.