This is using public office for personal gain

No that's your bias assumption. 2 things can be true at once. It can benefit Trump politically AND protect the country from criminal candidates at the exact same time.

Are we not? It's like if he witheld money from Hawaii and told them to reinvestigate Obama's birth certificate. There's only one interpretation at this point.

Yes we want to make sure it's real and done by non bias investigators. That is what internal affairs do with police all the time. That doesn't fucking mean we want fake evidence we just want to see if any real evidence has been overlooked or hidden.

Where is this proof?

That is what the investigation is trying to find.