The Ds want to shred the Constitution -- selectively.
Rand Paul made an impassioned speech (which is on TouTube) about how this trial is unconstitutional because Trump is no longer the President. The Ds argument is that because one of the penalties of a conviction, in addition to removal from office, can be a ban on holding office in the future, the trial is constitutional. But the Constitution says a trial pursuant to impeachment shall be presided over by the Chief Justice.
The Ds have appointed a rabid anti-trump D to preside. So their position comes down to cherry picking: The Constitution allows the trial to proceed even though Trump is no longer President, but because Trump is no longer President the part about rhe Chief Justice doesn't apply.
Blatant hypocrisy. But ... I repeat myself.