[SoConPubbie]

Those, however, weren't from Trump himself -- and Trump's personal involvement raises the stakes if the message was intended to impact a witness' testimony

Except this isn't a trial, so that statement was a lie.

[pierrem15]

Exactly. There’s no such as “witness tampering” because this isn’t a trial. Or it is, in which case the whole committee is acting violation of the Constitution and is trying in effect to pass a bill of attainder.

[DoodleDawg]

Except this isn't a trial, so that statement was a lie.

You can be charged with witness tampering if the witness is testifying in any official proceeding and not just a trial. But since the person in question never answered the call we have no idea what Trump would have said to them so I don't see where proving tampering is at all possible.