http://thefederalist.com/2018/08/03/sen-dianne-feinsteins-personal-driver-20-years-chinese-spy/
5 years ago, to be precise. FBI came and told her about her driver. No FISA then, certainly too long ago to get a FISA warrant against anyone now, at least about that driver. Are there any other spies in her office?
If they had a FISA warrant on her they would not reveal it for this mess... they would be more interested in who the information is leaking to on the Chinee side.