The senator says the investigation is a fishing expedition by his enemies to see if they can find anything he has ever done that might hurt his political career.

• 这段话说:那位参议员声称,这次调查是他政敌的蓄意盘查,目的是搜罗挖掘他是否有不端行为,以便损毁他的政治生涯。所以fishing expedition是指以搜罗挖掘不利于某人的证据为目的的调查行动。