Twitter posts hardly rise to the level of crimes that justify impeachment.
Twitter is another form of public speech. There is no difference between twitting these accusations or holding a press conference.
False speech must have consequences. Trump advocated as much during his campaigning.
Is there no straw too frail for the left to try to grasp?
So you are advocating for accountability-free presidency? Do you understand that if Trump isn't held to answer, no POTUS ever again will be bound to tell truth? You can cynically point that all politicians brake promises, but promises is not the same thing as lying about factual events.
For example, 2020 some Democratic populist gets elected on the wave of "anyone but Trump". Then they falsely declare that GOP was putting LBGT people into concentration camps, then proceed to drive policy from that point (anti-hate speech laws, reconciliation and compensation and so on... basically raining taxpayers money on anything LBGT and making it illegal to speak out against this). Would you want to live in such US? If not, hold Trump accountable.