Now sure Trump can veto legislation put forward by Congress, but that is not what they are impeaching him for. They are impeaching him because the administration had refused to cooperate with the Congressional investigation, by withholding documents and testimony from key persons. How would Republicans have reacted if Clinton had refused to talk to the Whitewater investigation? Saying "fine, that's his right as the President"?
Now Trump has also given Dems plenty of ammo, by saying "there was no quid pro quo" when testimony from others have later shown that a visit to the White house (and perhaps the military aid) was conditioned on Zelensky announcing an investigation into Burisma, not just starting it
I am the Demon of Delightfulness and Sinister Smirkings!
e^(πi)+1=0
identity named after the Terry Pratchett of 18th century mathematics