Was Princess Di conversing with terrorists, or did she talk with someone here in the USA?
As far as the surveillance laws then in effect are concerned, there is likely to be a distinction.
Whether Klintoon personally authorized it is beside the point. Rather, was there a national security issue involved?
Klinton spied on everyone then, which is how he kept people in check and destroyed his enemies. Remember when he announced that Bob Hope had died, and it turned out he hadn't, but he almost did? That had to have come from an intercept.