One group says a president can be impeached only while in office. “I tend to believe it is only for current office holders,” said Harvard law professor Cass Sunstein, author of “Impeachment: A Citizen’s Guide. ”

According to a second group of scholars, if the House votes to impeach while the president is in office, the Senate can proceed to a trial even after the president has left office.

“Once an impeachment begins in the House, it may continue to a Senate trial. I don’t see any constitutional problem with the Senate acting fast or slowly,” said Michael Gerhardt, a law professor at the University North Carolina at Chapel Hill.

And a third view is that the entire process can begin even after the president is out of office.