Note: No one...either Republicans or Democrats serving in Congress seems to have raised this question regarding whether or not he can be tried in the Senate once out of office. I would tend to say "no," but the only thing I remember McConnell objecting to was the timing of the trial and how quickly it could be done. That tells me that no one is objecting to the trial itself...but I'm not sure what the grounds are for that position? Since no President has ever been convicted on impeachment (3 have been impeached, Trump twice), we're usually breaking new ground with Presidential impeachments and the subsequent trial. But there have been convictions on impeachment of federal judges. The problem there, in comparing the judges to presidential impeachments is that federal judges are appointed for life and Presidents are elected to specific 4 yr terms. I believe there has been one federal judge removed from office, but who subsequently was elected to the House and allowed to serve. Maybe House rules trumped (pardon the pun) the loss of the federal judgeship? Remember there is a clause in the Constitution allowing both the Senate and House to set their own rules, which could have practically the effect of an elected representative sit in the chamber, but without power (i.e. deprived from committee assignment, denied caucus membership, etc.). Maybe someone else knows more and can explain. Oh yeah...there was a Cabinet officer who knowing he was going to be impeached and convicted, so he resigned before it happened. Congress impeached him anyway, on the reasoning that his resignation was to avoid the dishonor of being impeached and possibly convicted him. Not sure if he was tried in the Senate or not?