While it's completely retarded I agree but what exactly makes it unconstitutional?
Impeachment Trials of Presidents must be presided over by the Chief Justice. The Chief Justice is not presiding over this "trial", therefore it is not an impeachment of a President.
But if the "trial" is not impeaching Trump as a President then who is it impeaching? If it is impeaching Trump as a private citizen then that is technically impossible, and becomes a Bill of Attainder, which is explicitly unconstitutional.
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