This is not merely a theoretical abuse of power; it's one to which the FBI itself has admitted.
So, Senator Durbin of Illinois introduced an amendment to the current FISA renewal act which would restrict the issuing of NSLs. The FBI would have to show that the records sought either (1) pertain to a foreign power, (2) are relevant to a suspected agent of a foreign power, or (3) pertain to an individual in contact with or known to a suspected agent of a foreign power. (Still no requirement to go to a court before conducting the 'search', though.)
Both Klobuchar and Franken voted against this amendment (HEN09A07). And according to the same source, Klobuchar appeared confused, first proclaiming her support for the language of the amendment and then voting against it.