There is no evidence that Trump with held assistance to Ukraine period. (heresy is not evidence, opinions are not evidence) It was delivered!
The direct evidence indicates the opposite. Sondland's testimony, the phone call transcript and Zelensky's response to questions.
Maybe Trump did request privately to have Biden and the DNC, Crowdstrike investigated, there was cause for concern. (see link)
https://www.foxnews.com/media/peter-schweizer-how-biden-family-got-rich
If Ukraine did the investigating as a favor to the POTUS or if Rudy Giuliani investigated the situation as his personal lawyer on behalf of the POTUS, BFD. It isn't costing the tax payers a penny.
Any hint of corruption by the VP or information of a server containing classified information should be investigated.