I feel certain, looking at the information in this new context, that the surveillance of Trump goes back to November 2015, when the big jump in NSA database queries began, coincidentally when Nellie Ohr began working for Fusion GPS.
Unmentioned in all this is what surveilance was carried out on the other Republican candidates?
Surely Jeb Bush was surveiled as the leading candidate in the early days of the campaign. Trump surveilance is but the observable part of the survelience ice berg