All three should be investigated. All three are hiding the truth. All must be thoroughly investigated.

1. Why did Trump ask Ukraine using his office to investigate a political opponent?
2. Why did Hunter Biden fly on Daddy's office trip and airplane and get introduced to Chinese corporations and get board appointments?
3. Why did Biden use his elected office to gain favors for his son? How is he different from Trump and his nepotism when Trump appoints his own children in adviser roles and takes daughter on all high visibility foreign official trips.

All three are lying and all must be called out. No need to defend any of these assholes.

I can only think it was Trump himself with the help of the people on his reelection campaign. It is not hard to imagine that Trump asked his people to dig up (or manufacture) dirt on his opponents (that's the way he rolls). And since Trump surrounds himself with "Yes" men (who probably operate on the same moral code as Trump), it is also not hard to imagine that they just go along with whatever Trump wants. Trump either believes himself to be above the law or he is too stupid to know when he is crossing the line.

Given historical corruption in Ukraine, the idea for fomenting "fake news" stories by/from Ukraine is kinda politics-as-usual.