Yep, been asking that question myself for months - who aside from Trump and Co. from the GOP has been surveiled? Also, how in 2014 could they know that Manafort would even become a part of Trump's campaign? Trump didn't announce until halfway through 2015.
Sir:
What I’m saying is that as soon as they could surveil Trump, they did. Probably not as early as 2014, but as soon as Manafort and Trump connected.
Manafort was probably being surveilled simply because he was involved in a part of the world the Democrats were economically interested in...Soros’ Ukraine project, etc.