The impeachment itself was disgraceful. No witness testimony, no evidence, no committee hearings, no due process. It was a rushed partisan act of revenge that sets a horrible precedent.
The impeachment trial is unconstitutional and unprecedented. Even holding such an illegitimate trial is shameful. There is not a word in the Constitution about the impeachment trial of former official. When President Nixon resigned, his impeachment was dropped by a near unanimous vote. Everyone believed it was unconstitutional to continue the impeachment after he was out of office. That is the relevant precedent.
The actual case against Trump is a confusing melange. Ok rioters riotted. What’s that got to do with Trump? The original theory he riled up the crowd to violence didn’t hold up. He urged the crowd to “peacefully and patriotically make your vouces heard”. Before he was through demonstrators were pushing barricades at the Capitol mile away. Then they try to confound speaking out against an election as sedition or insurrection as if they hadn’t spent four years railing against 2016 election. Then without evidence or witnesses, they concoct a slickly edited lie that Trump directed the extremist groups which pre-planned unlawful entry into the Capitol.
I also agree the impeachment trial is a horrible mistake. Once established as precedent, you can expect a slew of quickie impeachments and Nazi-style show trials for hordes of ex- officials with each change in electoral fortunes.