When your argument falls back to “yeah well you can’t prove it” it’s time to reconsider the strength of your argument.
You can't get much of a stronger argument than that. So far, this entire impeachment is about mind reading. The Democrats were able to read Trump's mind on why he withheld aid. The Democrats were able to read minds to know that Biden would be their nominee a year ahead of time. The Democrats read minds to tell us what Shokin did, instead of him telling us what he did. The Democrats were able to read Zelensky's mind when he said he felt no pressure from President Trump.
It's all about mind reading, and the Democrats impeached on it. So don't tell me I have a weak case.