There are no timing limitations on the use of the Impeachment process in the Constitution. So there is no limit in the Constitution for impeaching someone after they have left office.
There are Senate and House rules regarding impeachment but rules can be changed with a majority vote.
The Constitution doesn't grant Congress the power to impeach a private citizen.
And it would look pretty stupid trying to remove somebody from an office that they don't hold.
LOL.
Wrong. The Constitution used the term PRESIDENT. If the person IS NOT THE PRESIDENT, THE LAW DOES NOT apply to the person.
The limit is that you can only impeach elected or Senate approved appointees. Trump will not be either in 10 days.
“There are Senate and House rules regarding impeachment but rules can be changed with a majority vote.”
Ex post facto