It’s unconstitutional.
“No Bill of Attainder or ex post facto Law shall be passed.”
Article I, Section 9, Clause 3, U.S. Constitution.
Congress lost the power to impeach once Trump left office.
No bill of attainder involved. Congress is empowered to impeach without involvement of a court. The narrow definition of “attainder” is legislature actinng without a court. By that definition, all impeachment would be bill of attainder. Impeachment is “okay” cause the penalty is limited and the penalty is not criminal.
No ex post facto violation. There is an issue about whether or not the alleged offience is impeachable, but that standard is up to Congress. What constitutes impeachable has no grounding in principle, other than purely academic arguments on both sides.
Once Trump left office he became a private citizen, and the Bill of Attainder prohibition then applied. He was only subject to impeachment because of his office. If he did something wrong, that’s now up to the civil and criminal judicial system, but the Constitution prohibits legislative trials.
This situation is pretty close to the classic bill of attainder. There, when a political faction fell out of power, Parliament would generally “attaint” them, strip them of their lands and titles, and then cut their heads off.
If this weren’t the standard, the next Republican Congress could go back and retroactively impeach Obama, Clinton and Carter, even though they’re long gone from office. Obviously that’s absurd although I can think of at least one valid article of impeachment against Obama (illegally transferring funds to Iran in violation of federal law).
Note, however, the “regicides” who participated in the execution of Charles I were later attainted even after their deaths, and the corpses were dug up and ritually executed.
Like they care.
Dem: That dusty old constitution thing again? Sheesh. I'm getting sick of hearing that legal stuff. Can't we get away with anything?