False premise. But you knew that. Consider this sequence: a person is impeached, convicted, removed from office. Only AFTER the person is out of office can there be a vote to block from further office. CLEARLY the Senate process, by design, continues after leaving office. Both Trump's impeachments occurred in the House while he was in office.
There is no such thing as a retroactive impeachment. Trump broke the law while pretending he was president*, he was impeached while he was still squatting in our White House. Nothing retroactive about it.
Destroyed the economy? The DJIA was 5,000 and unemployment was about 8% when Obama took office. The DJIA was 20,000 and unemployment about 4% when he left. Obama inherited a recession, and turned it around. trump inherited an economy on the rise, and claimed credit. The sad thing is some trump supporters are stupid enough to believe him.
And trump was in office when impeachment proceedings began. He also committed impeachable offenses. Obama is no longer in office, and there is no evidence that he committed impeachable offenses.