I guess I missed the part where it was concluded that the Trump campaign was connected to Russia. But go on.
Surveillance on the opposing partys candidate by the sitting president would be one of the worst abuses of power in the history of this country.
If it's incidental collection when he wasn't the target that would be fine. Also if it were done via warrant that would be ok. I do feel though that if it were part of an investigation of something like hacking by the Russia government it would absolutely be legitimate. The only way it would be wrong would be if it were simply a fishing expedition.