If Trump really thought the Bidens were criminals, and he needed Ukraine's help to get evidence, he would have asked the FBI to contact the Ukrainian embassy under a Mutual Legal Assistance Treaty. That is the proper channel for such a request.
We need to impress upon people, this is way outside the boundaries of how a reasonable officer of the U.S. would use their power.
It's literally the one thing the Founders feared, above all, a president would do! What they said in the Federalist Papers is the worst case scenario!