Article I of the Constitution broadly grants the Senate “sole power to try all impeachments” and provides that “no person shall be convicted without the concurrence of two-thirds of the members present.” But the Constitution does not specify the manner in which the Senate must take that vote.
In the absence of any specific Constitutional direction, Senate Majority Leader Mitch McConnell will have broad discretion to determine how a vote will take place at the end of a Senate trial. He may feel that if the vote is held in private, Senators from both parties will be more likely to vote their true conscience and to break from party lines.
But both precedent and politics favor an open, public vote. In terms of precedent, the Senate impeachment trials of Andrew Johnson and Bill Clinton both concluded with open, public votes. And politically, it likely will be difficult for McConnell and other Senators to justify anything but open, transparent, Senator-by-Senator voting. Impeachment and conviction are too important for Senators to hide behind the cloak of anonymity.