Lets assume they move forward on this, only to prevent Trump from running on 2024 based upon a law that does not exist yet. Whats to stop Trump from resigning just before the vote and avoiding an impeachment? I know these bastards will probably impeach him retroactively.
I've remarked elsewhere that this is an option and in fine Trump style. Outfox them at the last hour by resigning, making Pence the shortest-term president ever, making impeachment moot, and leaving Pence with the nasty work of attending the inauguration of the faux potus. Then a well-deserved vacation and plans for 2024.
Trump's political support has pretty much evaporated at this point and the senate will convict him regardless because they are petty spineless jerks. But they will give speeches that they are saving the country and doing the righteous thing.
You do not have to be currently in office to be impeached.
Impeachment (originally) was a tool of Parliament to PREVENT the King from naming a minister that Parliament did not want.
That conviction can be followed by a ban of holding office IN THE FUTURE indicates that anyine could be impeached, tried, and convicted for treason, bribery, or any other "high crime and misdemeanor".