It likely started the day he questioned th BC.
You are probably right.
“It likely started the day he questioned the BC.”
Trump was pushing the Birth Certificate issue in early 2011. I agree that that would have probably kicked their attack dogs into action. He also said he was thinking about running for President then as well. I assume that they were abusing all the powers of their office as hard as they could, all along. So they probably started illegally spying on Trump in 2011, if not sooner (although that may never be proven).
That timeframe would have given them lots of time to plant leads and gradually sic allied Nations Intelligence Services on their political enemy as well.